Y3 


THE   ORIGINAL   BABCOCK   TESTER 


Modern  Methods 
of  Testing  Milk  and 
Milk  Products 


A  HANDBOOK  PREPARED  FOR  THE  USE  OF  DAIRY 
STUDENTS,  BUTTER- MAKERS,  CHEESE-MAKERS,  PRO- 
DUCERS OF  MILK,  OPERATORS  IN  CONDENSERIES, 
MANAGERS  OF  MILK-SHIPPING  STATIONS,  MILK- 
INSPECTORS,  PHYSICIANS,  ETC.  :::  :::  :::  :::  ::: 


By 

LUCIUS    L.  VAN  SLYKE 

Chemist  of  the  New  York  Agricultural  Experiment  Station 


ILLUSTRATED 
SECOND  REVISED  EDITION 


NEW   YORK 
ORANGE  JUDD  PUBLISHING  COMPANY 

LONDON 

KEGAN  PAUL,   TRENCH,  TRUBNER  &  Co.,   LIMITED 
1922 


COPYRIGHT,  1906,  1907,  1912,  BY 

ORANGE  JUDD  COMPANY 

All  Rights  Reserved 


[ENTERED  AT  STATIONERS'  HALL,  LONDON,  ENGLAND] 


[Printed  in  U.  S.  A.J 


PREFACE 

To  attain  the  highest  degree  of  success  in  the  pro- 
duction of  milk  and  in  the  manufacture  of  its  pro- 
ducts, it  has  become  essential  to  acquire  some  knowl- 
edge of  the  methods  of  testing  milk  and  milk  products. 
The  application  of  these  methods  to  dairying  has  re- 
sulted in  lifting  the  dairy  industry  to  a  higher  plane 
of  intelligence,  and  in  effecting  changes  of  great 
economic  importance,  among  which  may  be  briefly 
mentioned:  (i)  Greater  justice  rendered  milk  pro- 
ducers in  paying  for  milk  according  to  its  quality.  (2) 
Prevention  of  large  losses,  once  very  common,  in  the 
manufacture  of  butter  and  cheese.  (3)  Improvement 
of  methods  of  manufacture  through  better  control  of 
details.  (4)  Increase  of  yield  of  products  made  from 
a  given  amount  of  milk.  (5)  Improvement  in  the  uni- 
formity and  quality  of  manufactured  dairy  products. 

This  little  book  has  been  prepared  for  the  use  of 
dairy  students,  cheese-makers,  butter-makers,  produc- 
ers of  milk,  operators  in  condenseries,  managers  of 
shipping-stations,  milk-inspectors,  and  others  inter- 
ested. Physicians  who  are  specialists  in  infant-feed- 
ing will  find  the  book  useful  in  testing  human  milk  as 
well  as  cows'  milk  that  is  modified  or  to  be  modified. 

No  previous  chemical  training  is  required  for  oper- 
ating successfully  the  methods  described.  Any  intel- 
ligent person  who  can  labor  with  painstaking  patience 
and  appreciate  the  value  of  attention  to  little  details 
should  be  able  to  master  these  methods  with  a  rea- 


VI  PREFACE 

sonable  amount  of  work.  The  assistance  of  a  trained 
teacher  will,  of  course,  make  the  task  easier.  No  one, 
whatever  his  educational  preparation,  can  hope  to  use 
these  or  any  similar  methods  successfully  who  can 
not  or  will  not  follow  instructions  accurately  and  ex- 
ercise patience  in  mastering  every  minute  detail. 

In  the  preparation  of  this  work,  the  writer  has  tried 
to  keep  in  mind  the  following  points:  (i)  Accuracy, 
simplicity  and  clearness  of  statement.  (2)  Making 
prominent,  as  far  as  practicable,  the  reasons  for  each 
step  in  each  process.  (3)  Emphasis  of  common  diffi- 
culties and  instructions  for  overcoming  them.  (4)  Im- 
pressing students  with  the  necessity  of  precision  and 
care  in  performing  every  detail  given.  (5)  Selection 
of  the  methods  approved  by  experience.  (6)  Avoidance 
of  such  technical  methods  as  require  unusual  skill  or 
equipment.  (7)  Omission  of  unnecessary  details.  (8) 
Embodiment  of  the  results  of  the  most  recent  investi- 
gations. (9)  The  special  needs  of  those  for  whose  use 
the  work  is  designed. 

The  scope  of  this  work  is  far  from  exhaustive,  but 
the  methods  selected  are  given  with  necessary  com- 
pleteness. Chemical  methods,  requiring  elaborate 
equipment  and  extended  special  training,  are  purposely 
omitted.  Any  one  desiring  a  full  description  of  such 
methods  can  obtain  it  by  addressing  a  request  to  the 
U.  S.  Department  of  Agriculture,  Bureau  of  Chem- 
istry, Washington,  D.  C,  asking  for  a  copy  of  "Meth- 
ods of  Analysis  adopted  by  the  Association  of  Official 
Agricultural  Chemists." 

The  methods  that  have  been  compiled  here  are  in 
large  measure  the  direct  result  of  the  work  of  our 


PREFACE  VU 

agricultural  experiment  stations,  and  afford  some  in- 
dication of  the  direction  and  value  of  the  work  done 
by  these  institutions. 

In  the  preparation  of  Chapter  2£VII,  valuable  assist- 
ance has  been  kindly  rendered  by  Mr.  George  A.  Smith, 
Dairy  Expert  of  this  station. 

L.  L.  VAN  SLYKE. 
New  York  Agricultural 
Experiment  Station,  1906. 


PREFACE 
TO  SECOND  REVISED  EDITION 

Five  years  have  passed  since  this  book  was  last  re- 
vised. During  these  few  years,  new  demands  have 
arisen,  and,  in  response,  new  methods  of  testing  milk 
and  milk  products  have  been  developed,  which 
are  in  constant  requirement  and  which  should, 
therefore,  be  readily  available.  Some  idea  of 
the  extent  and  direction  of  the  activity  in 
these  lines  can  be  gathered  from  the  number 
and  character  of  the  changes  introduced  in  the 
present  edition.  Without  going  into  details,  it  is 
sufficient  to  say  that  four  chapters,  consisting  .almost 
entirely  of  new  matter,  have  been  added,  and  several 
other  chapters  have  been  completely  rewritten  and  en- 
larged by  incorporation  of  much  .additional  material, 
while  in  only  a  few  chapters  has  there  been  no  appre- 
ciable change.  It  has  been  desired  to  make  the  re- 
vision sufficiently  thorough  to  bring  the  subject  mat- 
ter fully  up  to  date. 

L.  L.  VAN  SLYKE. 

Geneva,  N.  Y.,  August,  1912, 


CONTENTS 


PAGE 

I 

Chemistry  of  Cow's  Milk  and  Milk  Products  ...         1 

II 

Methods  of  Sampling  and  Preserving  Milk       ...       20 

III 
The    Babcock   Test — Description   of   Apparatus    and 

Materials       32 

IV 
Method  of  Operating  the  Babcock  Test 57 

V 
Method  of  Testing  Cream  by  the  Babcock  Test     .     .       73 

VI 
Methods  of  Testing  Skim-milk,    Buttermilk,    Whey, 

Ice-Cream,  Condensed  Milk  and  Powdered  Milk      93 

VII 
Methods  of  Testing  Butter  and  Cheese  for  Fat    .     .     101 

VIII 
Methods  of  Testing  Butter  for  Water     ......     110 

IX 
Methods   of  Testing   Butter   for   Salt 125 

X 

Methods  of  Testing  Acidity  of  Milk  and  Milk  Pro- 
ducts             .     .     131 

ix 


X  CONTENTS 

PAGE 
XI 

Methods  of  Testing  the  Sanitary  Condition  of  Milk     152 

XII 
Methods    of    Testing    Milk    by    Rennet-Extract    and 

Pepsin 169 

XIII 
Methods   of  Testing  Specific   Gravity  and  Solids   of 

Milk    by    the    Lactometer 175 

XIV 
Methods  of  Testing  Milk  for  Casein 189 

XV 

Methods    of   Testing    Milk   and    Milk    Products    for 

Adulterations 201 

XVI 
The  Babcock  Test  applied  to  Farm  Conditions    .    .    211 

XVII 
Methods    of    Commercial    Testing    and    Scoring    of 

Butter  and  Cheese 218 

XVIII 
Methods  of  Commercial  Testing  and  Scoring  of  Milk 

and  Cream 242 

XIX 

Arithmetic   of  Milk  and  Milk  Products 253 

Appendix       L. ^     .     .     .    275 

Index  279 


ILLUSTRATIONS 


PAGE 

The  Original  Babcock  Tester Frontispiece 

Composite-Sample  Jars 25 

Rack  for  Composite  Samples 26 

Sampling-Dipper          &  27 

Scovell  Milk-Sampler 27 

Equity  Milk-Sampler ^  27 

Milk-Testing   Bottles 34 

Milk-Measuring   Pipette 35 

Greiner's   Automatic    Pipette ...  37 

Wagner's    Pipette 37 

Acid-Measure ^     .     .     .  37 

Acid-Burette    and    Stand 38 

Automatic    Burette     ....     :.      ......  38 

Steam-Turbine    Tester .  39 

Hand-Tester 39 

Small    Hand-Tester 40 

Electric    Centrifuge 41 

Hydrometer  for  Testing  Strength  of  Sulphuric  Acid  44 

Milk-Bottle    Tester .  49 

Testing  Accuracy  of  Milk-Bottle A  49 

Burette    and    Support    .     , ...,..».  52 

Waste-Jar  for  Emptying  Test-Bottles    ......  53 

Test-Bottle    Rinser     .     , 54 

Test-Bottle  Draining-Rack 54 

Farrington's  Bottle-Cleaner— Bottle-Holder  Empty  .  55 

Farrington's  Bottle-Cleaner — Bottle  Holder  Immersed  56 

Farrington's  Bottle-Cleaner — Bottle-Holder  Draining  56 

Correct  Way  of  Holding  Pipette  and  Bottle   ...  59 

Wrong  Way  of  Holding  Pipette  and  Bottle   ...  60 

xi 


Xll  ILLUSTRATIONS 

PAGE 

Measuring  Fat-Column 67 

Automatic  Russian  Pipette  ...     tf      ......  71 

Russian  Test-Bottle .  71 

Straight-Necked    Cream-Bottles   ^ 75,  75 

Bulb-Necked    Cream-Bottle      .....'.     tt     ...  -77 

Cream-Testing    Scales 79,  80 

Combined    cream-stirrer   and    sampler    ........  82 

Cream-Sampling   Sieve    .      . 86 

/"Bottles  for  Testing  Skim-Milk     ........  94 

Bottle  for  Testing  Butter :.     .     .  103 

Shaw's    Butter-Test    Apparatus    .     .     .     .     .        104",  105 

Benkendorf  Oven 117 

Farrington's    High-Pressure    Oven 118 

Gray's  Moisture-Test  Apparatus 123 

Van    Norman's   Acid-Test 142 

Farrington's    Alkaline-Tablet    Test 143 

Spillman's    Acid-Cylinder L.  144 

Convenient  Apparatus  for  Acid  Testing  ...     .     .     .  145 

Publow    Acid    Test    .     &     .     .     .......  146 

Marschall  Acid  Test '.     .  147 

Wisconsin  or  Lorenz  Dirt-Tester 165 

Hand-Centrifuge  for  Sedimentation  Work  ....  166 

Tube    for    Sedimentation   Work    .     ...     .     .     .  166 

Bausch  &  Lomb  Electric  Centrifuge 166 

International  Instrument  Co's  Electric  Centrifuge    .  167 

Glass  for  Collecting  Sediment  in  Milk              .     .  168 

Monrad    Rennet-Test       . 169 

Marschall   Rennet-Test    .     ...     a     ......  171 

Quevenne    Lactometer    ..........  178 

Cylinder  for   Lactometer 181 

Comparison  of  Different  Specific  Gravity  Scales  .      .  182 

Richmond's    Slide-Rule 186 

Apparatus  for  Volumetric  Casein  Test  .     .     ,     .     .  193 

Butter-Trier      ,     .     .    ±    *    .     .    A    .    *    *    .     .  219 


Modern   Methods  of  Testing  Milk 
and    Milk    Products 


CHAPTER   I 

Chemistry  of  Cow's  Milk  and  Milk  Products 

THE  normal  milk  of  cows  contains  the  following 
compounds  and  classes  of  compounds: 

(1)  Water.  (4)   Milk-sugar. 

(2)  Fat.  (5)  Salts  or  ash. 

(3)  Nitrogen  compounds  or  proteins.    (6)  Gases. 

WATER 

The  water  present  in  milk,  however  much  its  pres- 
ence may  be  disguised,  is  the  compound  of  hydrogen 
and  oxygen  with  which  we  are  everywhere  familiar. 
The  water  in  milk  serves  the  purpose  of  holding  in 
solution  the  soluble  constituents  of  the  milk,  and  it 
also  acts  as  a  diluent,  better  fitting  the  mixture  for 
animal  nutrition. 

Variation. — The  amount  of  water  normally  con- 
tained in  milk  varies,  depending  upon  such  conditions 
as  individuality,  breed,  stage  of  lactation,  age,  char- 
acter of  food,  amount  of  water  drunk,  state  of  health, 
etc.  In  the  case  of  single  milkings  of  individual  cows, 
the  water  may  vary  from  82  to  90  per  cent,  or  more. 
In  the  case  of  milk  from  herds  of  cows,  the  water 
varies  less,  usually  ranging  from  86  to  88  per  cent. 


MODERN    METHODS   OF   TESTING    MILK 

The  influence  of  breed.— The  following  figures, 
from  the  records  of  the  N.  Y.  Agricultural  Experi- 
ment Station  at  Geneva,  illustrate  the  influence  of  breed 
upon  the  water  content  of  milk : 

Per  cent,  of 
NAME  OF  BREED  water  in  milk 

Holstein  Friesian 88.20 

American  Holderness 87.35 

Ayrshire 87.25 

Short  Horn 85.70 

Devon 85.50 

Guernsey 85.10 

Jersey 84.60 

The  influence  of  lactation. — The  variation  of  water 
in  milk,  as  affected  by  advance  of  the  lactation  period, 
is  illustrated  by  the  following  figures,  which  cover  a 
period  of  ten  months  from  the  time  of  calving: 

Per  cent,  of 

MONTH  OF  LACTATION                                              water  in  milk 
i 86.00 

2 86.50 

3 86.53 

4 86.36 

,5 86.25 

6 86.00 

7 85.82 

8 .     .     .  85.67 

9 85.54 

10 85.17 

There  is  noticeable  a  general  tendency  for  the 
amount  of  water  in  milk  to  increase  for  the  first 
three  months  of  lactation,  after  which  there  is  a  con- 
tinuous decrease  to  the  end  of  the  lactation  period. 


CHEMISTRY   OF   COWS     MILK  3 

Total  solids. — Under  the  general  term  of  total  solids 
or  milk-solids,  we  indicate  the  constituents  of  the  milk 
other  than  water  (and  gases).  The  per  cent,  of  water 
in  milk  subtracted  from  100  gives  the  percentage  of 
milk-solids,  which  include  fat,  proteins,  milk-sugar 
and  salts  or  ash.  The  amount  of  solids  in  milk  varies 
with  the  same  conditions  that  affect  the  percentage 
of  water  in  milk,  but,  of  course,  in  just  the  reverse 
manner.  Most  states  orescribe  a  legal  standard  for 
milk-solids,  usually  12  per  cent.,  and  milk  containing 
less  than  the  legal  amount  is  regarded  as  adulterated. 

MILK-FAT 

The  composition  of  milk-fat. — Milk- fat,  also  called 
butter-fat,  is  not  a  single  chemical  compound,  but  is 
a  somewhat  variable  mixture  of  several  different  com- 
pounds called  glycerides.  Each  glyceride  is  formed  by 
the  chemical  union  of  glycerin  as  a  base  with  some 
acid  or  acids  of  a  particular  kind.  These  glycerin-acid 
compounds,  or  glycerides,  of  milk-fat  contain  about 
ten  different  acids,  some  being  present  in  small  propor- 
tions. The  four  following  acids  enter  most  largely 
into  the  composition  of  milk-fat,  in  the  form  of  their 
combinations  with  glycerin:  Palmitic  acid,  oleic  acid, 
myristic  acid  and  butyric  acid.  The  compounds,  or 
glycerides,  formed  by  the  combination  of  glycerin  and 
the  acids,  have  special  names  derived  from  the  acids; 
thus,  we  have  palmitin  (glycerin  combined  with  palm- 
itic acid),  butyrin  (glycerin  combined  with  butyric 
acid),  olein,  etc.  Milk- fat  contains,  on  an  average, 
about  40  per  cent,  of  palmitin,  34  per  cent,  of  olein, 
10  per  cent,  of  myristin.  6  per  cent,  of  butyrin,  and 


4  MODERN    METHODS   OF   TESTING   MILK 

from  less  than  i  to  nearly  3  per  cent,  of  each  of  the 
glycerides  of  other  acids.  Milk-fat  contains  about 
12.5  per  cent,  of  glycerin  in  combination  with  the 
acids.  The  proportions  of  these  constituents  of  milk- 
fat  vary  somewhat,  and  this  variation  influences  the 
character  of  the  milk-fat.  Thus,  palmitin  and  myris- 
tin  tend  to  make  milk- fat  harder,  while  olein  and  buty- 
rin  have  the  opposite  tendency. 

The  acids  contained  in  milk-fat  or  butter-fat  may 
be  divided  into  two  groups:  (i)  The  acids  in  one 
group  (palmitic,  oleic,  myristic,  stearic,  lauric)  are 
insoluble  in  water  and  non-volatile,  while  (2)  the 
other  acids  (butyric,  caproic,  etc.,)  are  more  or  less 
completely  soluble  in  water  and  are  volatile.  These 
differences  afford  a  practical  basis  for  distinguishing 
pure  butter  from  artificial  butter.  Of  the  fat-acids 
contained  in  butter-fat,  about  87.5  per  cent,  consists 
of  the  insoluble  fat-acids,  while  in  other  forms  of 
animal  fat  (beef- fat,  lard,  etc.,)  the  amount  of  these 
insoluble  fat-acids  is  considerably  greater.  The  amount 
of  volatile  fat-acids  in  milk-fat  or  butter-fat  is  much 
greater  than  in  other  forms  of  animal  fat. 

Fat-globules  in  milk. — Milk-fat  is  present  in  milk, 
not  in  solution,  but  suspended  in  the  form  of  very 
small,  transparent  globules.  Globules  varying  in  size 
between  one  twenty-five  hundredth  and  one  fifteen- 
thousandth  of  an  inch  in  diameter  are  the  ones  most 
commonly  present.  The  average  size  of  fat-globules 
in  milk  is  somewhat  more  than  one  ten-thousandth  of 
an  inch  in  diameter.  The  smaller  globules  are  more 
numerous  than  the  larger  ones.  In  one  drop  of  aver- 
age milk  there  are  more  than  one  hundred  million  fat- 


CHEMISTRY   OF   COWS     MILK  5 

globules.  Skim-milk  contains  fewer  and  smaller  glo- 
bules than  whole  milk,  while  the  reverse  is  true  of 
cream.  The  large  globules  do  not  differ  in  composi- 
tion from  the  small  ones.  The  size  and  number  of 
fat-globules  in  milk  are  influenced  by  such  conditions 
as  advance  of  lactation,  breed  of  cow,  food,  age, 
health,  different  milkings,  different  parts  of  the  same 
milking,  etc. 

It  was  formerly  believed  generally,  and  is  still  by 
some,  that  the  fat-globules  of  milk  are  surrounded  by 
a  membranous  covering,  or  else  by  a  semi-liquid,  al- 
buminous layer.  We  may,  however,  accept  it  as  es- 
tablished beyond  reasonable  doubt  that  the  fat-globules 
of  milk  have  no  special  covering  of  any  kind,  but  are 
simply  minute  particles  of  fat  floating  free  in  milk  in 
the  form  of  an  emulsion.  Fat-globules  quite  generally 
retain  their  individuality  even  in  butter  and  cheese. 

Amount  of  fat  in  milk. — Normal  milk  varies  greatly 
in  its  fat  content,  containing  from  below  2  to  over  10 
per  cent.,  if  we  consider  single  milkings  of  individual 
cows.  The  milk  from  herds  of  cows  varies  in  fat 
more  commonly  between  the  limits  of  3  and  5  per 
cent.  The  average  amount  of  milk-fat  in  milk  pro- 
duced in  this  country,  taking  the  true  average  for  the 
entire  year,  lies  somewhere  near  4  per  cent.,  perhaps 
a  little  under.  Many  of  the  conditions  that  affect  the 
percentage  of  fat  in  milk  are  fairly  well  known,  while 
others  are  little  understood.  We  will  briefly  consider 
some  of  the  well-recognized  conditions  that  influence 
the  fat  content  of  milk. 

(i)  Influence  of  individuality  of  cow  on  fat  con- 
tent of  milk. — It  is  uncommon  to  find  in  a  herd  of 


O  MODERN    METHODS   OF   TESTING    MILK 

cows  two  individuals  whose  milk  contains  the  same 
per  cent,  of  fat,  whether  we  consider  single  milkings 
or  the  average  of  many  milkings. 

(2)  Influence  of  breed  of  cow  on  fat  content  of 
milk. — It  is  well  known  that  the  per  cent,  of  fat  in 
milk  varies   in  a   somewhat   characteristic   way   with 
the  kind  of  breed  of  cow.     While  there   is  marked 
variation  in  individuals  of  the  same  breed,  there  is 
found  to  be  a  fairly  uniform  difference,  more  or  less 
marked,  if  we  consider  the  averages  of  several  indi- 
viduals.     It  is   largely  owing  to   this   influence   that 
we  find  the  milk  of  one  country  differing  from  that 
of  another,  or  the  milk  of  one  section  of  a  country 
differing  from  that  of  another  section.     For  example, 
the  average  amount  of  fat  in  milk  in  Germany  and 
Holland  is  fully  one-half  per  cent,  lower  than  in  this 
country,  because  the  prevailing  breeds  of  cows  there 
are  those  producing  milk  comparatively  low  in   fat. 
The  following  figures,  taken  from  the  records  of  the 
New  York  (Geneva)  Agricultural  Experiment  Station, 
represent   averages   of   many   individuals    for   several 
periods  of  lactation :  Per  cent  Of 

fat  in  milk 
NAME  OF  BREED  Average  Lowest  Highest 

Holstein  Friesian 3-36  2.88  3.85 

Ayrshire 3-6o  3.20  4.24 

American  Holderness  ....  373  349  3-92 

Short  Horn 4-44  4-28  4.56 

Devon 4-6o  4-3°  5.23 

Guernsey 5-3Q  4-51  6.13 

Jersey 5-6o  4.96  6.09 

(3)  Influence   of  age   of   cow   on   fat   content   of 
milk. — So  far  as  published  data  throw  light  upon  this 


CHEMISTRY   OF   COWS'    MILK  7 

point,  there  appears  to  be  a  tendency  for  milk  to  be- 
come less  rich  in  fat  with  each  succeeding  period  of 
lactation,  especially  after  the  second,  though  individ- 
ual exceptions  are  not  infrequent.  More  data  are 
needed  to  settle  the  question  definitely. 

(4)  Influence  of  advance  of  lactation  on  the  fat 
content  of  milk. — In  general,  it  is  found  that  the  per 
cent,  of  fat  in  milk  increases  as  the  stage  of  lactation 
advances  after  the  third  month,  as  illustrated  by  the 
following  data  from  the  records  of  the  New  York 
(Geneva)  Station,  covering  10  months  from  the  time 
of  calving: 

NUMBER  OF  Per  cent,  of 

MONTH   OF  LACTATION  fat  IH  milk 

I .      4-54 

2 4-33 

3 4-28 

4 439 

5 438 

6 453 

7 456 

8   . 466 

9 479 

10 5.00 

(5)  Variation   of  time   between  milkings  in  rela- 
tion to  the  fat  content  of  milk. — As  a  rule,  the  longer 
the  time  between  two  successive  milkings,  the  smaller 
is  the  per  cent,  of  fat  in  the  milk ;  and  the  shorter  the 
time  between  milkings,  the  greater  the  per  cent,  of  fat. 
When  the  time  between  milkings  is  uniformly  equal, 
the  variation  of  fat  in  milk  is  small,  provided  the  gen- 
eral environment  of  the  animal  is  the  same.     How- 
ever, as  there  are  not  commonly  such  entirely  uniform 


8  MODERN    METHODS   OF   TESTING   MILK 

conditions  of  surroundings  during  the  day  and  night, 
there  appears  to  be  a  common  tendency  for  the  pres- 
ence of  a  little  more  fat  in  the  morning's  milk,  even 
when  milkings  are  apart  the  same  length  of  time. 

(6)  Variation  of  fat  content  in  different  portions  of 
milk  drawn  from  the  udder. — The  following  figures, 
taken  from  the  writer's  records,  illustrate  the  general 
rule  that  the  first  milk  drawn  contains  least  fat,  the 
milk  last  drawn  (stoppings)  being  the  richest  in  fat: 

Per  cent,  of  fat  in  milk 
cow  i    cow  2    cow  3 

First  portion  drawn  ....  0.90  1.60  1.60 
Second  portion  drawn  .  .  .  2.60  3.20  3.25 
Third  portion  drawn  ....  5.35  4-io  5«oo 
Fourth  portion  drawn  (strip'gs)  9.80  8.10  8.30 

It  is  also  known  that  the  per  cent,  of  fat  in  milk 
varies  in  different  quarters  of  the  udder  of  a  cow,  and 
also  varies  more  or  less  in  each  quarter  with  the  order 
in  which  the  teats  are  milked. 

THE    NITROGEN    COMPOUNDS    OF    MILK 

Some  confusion  prevails  in  respect  to  the  names  of 
the  nitrogen  compounds  of  milk.  They  have  been 
spoken  of  as  albuminoids,  proteins,  etc.  Frequently 
the  word  casein  is  erroneously  used  to  include  all  the 
nitrogen  compounds  of  milk. 

How  many  nitrogen  or  protein  compounds  are  pres- 
ent in  normal  milk  ?  What  are  they  ?  Different  work- 
ers have  reported  from  one  to  seven  or  more.  The 
chemical  evidence  at  hand  justifies  us  in  the  belief  that 
normal  milk  contains,  in  appreciable  amounts,  not 
more  than  three  nitrogen-containing  or  protein  bodies, 


CHEMISTRY    OF    COWS'    MILK  9 

viz.,  casein,  albumin  and  globulin.  Globulin  is  present 
in  so  small  quantities  that  we  can  properly  regard 
casein  and  albumin  as  being  essentially  the  nitrogen 
compounds  of  milk,  when  we  consider  them  quanti- 
tatively. 

Milk-Casein  is  the  most  important  nitrogen  com- 
pound in  milk,  because,  (ist)  it  is  the  one  present  in 
largest  quantity;  (2d)  its  presence  makes  it  possible 
to  convert  milk  into  cheese;  and  (3d)  it  has  a  high 
value  as  food.  Milk-casein  is  most  familiar  to  us  in 
the  form  of  the  solid,  white  substance  called  curd, 
which  forms  in  milk  when  it  sours,  though,  strictly 
speaking,  this  well-known,  white  substance  is  not  milk- 
casein,  but  a  closely  related  compound. 

(1)  Composition  of  milk-casein. — Casein  is  a  very 
complex  chemical  compound,  containing  the  elements 
carbon,  oxygen,  hydrogen,  nitrogen,  sulphur,  and  phos- 
phorus. In  milk  the  protein  molecule  of  casein  is  com- 
bined with  calcium,  or  some  calcium  compound,  and 
hence  the  proper  chemical  name  of  milk-casein   is 
calcium  casein.    It  exists  in  milk,  not  in  solution,  but 
in  the  form  of  extremely  minute,  solid,  gelatinous  par- 
ticles in  suspension.    The  slime  found  in  the  bowl  of 
centrifugal .  separators  consists,  to  a  considerable  ex- 
tent, in  milk-casein. 

(2)  Action  of  acids  upon  milk-casein. — When  milk 
sours  in  the  ordinary  way,  the  lactic  acid  formed  acts 
upon  the  calcium  casein,  two  chemical  changes  taking 
place.     First,  the  lactic  acid  combines  with  the  cal- 
cium of  the  calcium  casein,  forming  calcium- free  ca- 
sein, or  simply  casein  set  free  from  its  combination 
with  calcium.    When  more  lactic  acid  forms,  the  sec- 


IO  MODERN    METHODS   OF   TESTING   MILK 

ond  change  takes  place,  the  free  casein  taking  up  the 
acid  without  definite  combination  and  forming  a  sub- 
stance which  is  familiar  as  the  curd  of  sour  milk.  Sim- 
ilar changes  occur  when  milk  is  treated  with  other 
acids,  such  as  hydrochloric,  acetic,  sulphuric,  etc.  Free 
casein  is  insoluble  in  water  and  also  in  very  dilute  acids 
at  ordinary  temperatures.  The  action  of  acids  on  cal- 
cium casein  and  on  free  casein  is  hastened  by  increase 
of  temperature.  Casein  dissolves  easily  in  an  excess 
of  acid,  forming  soluble  casein  salts. 

(3)  Action  of  alkalis  on  milk-casein. — Dilute  solu- 
tions of  alkalis  (caustic  soda,  ammonia,  etc.)  act  upon 
casein  and  its   salts   with  acids,   forming  compounds 
that  dissolve  easily  in  water.    These  alkali  compounds 
of  casein  are  not  affected  by  rennet.     Some  of  these 
compounds  are  found  in  commerce  as  food  and  me- 
dicinal preparations  under  such  names  as   Plasmon, 
Nutrose,  Santogene,  Eucasein,  Galactogene,  etc. 

(4)  Action  of  heat  on  milk-casein. — Heat  alone  un- 
der ordinary  conditions,  even  at  the  boiling  point  of 
water,  does  not  coagulate  the  casein  in  milk.     Casein 
may  be  coagulated  by  heating  under  pressure  at  a  tem- 
perature of  about  270°    F.     The  browning  of  milk 
heated  under  pressure  is  more  or  less  due  to  changes 
in  the  casein.     The  formation  of  a  peculiar  skin  on 
the  surface  of  milk  heated  above  140°   F.  is  largely 
due  to  the  calcium  casein  of  the  milk  and  not  to  albu- 
min as  was  formerly  supposed.     The  skin  itself  con- 
tains practically  all  of  the  constituents  of  the  milk  and . 
may  be  regarded  as  a  kind  of  evaporated  milk. 

(5)  Action  of  rennet  on  milk-casein. — One  of  the 
most  characteristic  properties  of  the  calcium  casein 


CHEMISTRY    OF    COWS'    MILK  II 

of  milk  is  its  coagulation  by  the  enzym  or  chemical 
ferment  contained  in  rennet,  which  is  an  extract  of  the 
mucous  membrane  of  a  calf's  stomach.  This  property 
makes  possible  the  manufacture  of  cheese  from  milk. 
The  curd  formed  by  the  action  of  rennet  is  called  para- 
casein  or,  more  properly,  calcium  paracasein.  There 
appears  to  be  only  slight  chemical  difference  between 
calcium  casein  and  calcium  paracasein.  The  coagula- 
tion of  calcium  casein  produced  by  rennet  is  quite  dif- 
ferent from  that  produced  by  acids.  Calcium  paraca- 
sein behaves  towards  acids  and  alkalis  much  like  cal- 
cium casein. 

(6)  Other  changes  caused  in  milk-casein. — Under 
the  action  of  chemical  reagents,  of  enzyms  and  of  va- 
rious organisms,  calcium  casein  and  paracasein  may  be 
changed  into  a  large  number  of  other  substances. 
Among  the  compounds  and  classes  of  compounds  thus 
formed  are  paranuclein,  albumoses,  peptones,  amides 
(crystallizable  bodies)  and  ammonia.  These  products 
are  never  found  in  normal  milk  as  it  leaves  the  cow, 
but  may  be  present  in  milk  that  has  stood  some  time. 

Milk-Albumin. — Milk-albumin  differs  from  milk- 
casein  in  composition  and  behavior.  Thus,  milk-albu- 
min (i)  is  not  acted  upon  by  rennet;  (2)  is  not  coag- 
ulated by  acids  at  ordinary  temperatures;  (3)  is  co- 
agulated by  heat  alone,  though  not  completely,  above 
160°  F. ;  and  (4)  is  in  solution  in  milk. 

Milk-Globulin — This  compound  is  present  only  in 
small  quantities  in  normal  milk  and  is  of  no  special 
importance,  so  far  as  known. 

In  connection  with  the  nitrogen  compounds  of  milk, 
we  will  refer  briefly  to  a  class  of  compounds  which 


12  MODERN   METHODS  OF  TESTING  MILK 

have  attracted  much  attention  in  recent  years,  namely, 
milk-enzyms.  These  are  present  in  very  small  amounts 
and  have  never  been  isolated  in  pure  forms  but  they 
are  thought  to  be  nitrogen-containing  compounds. 
They  are  chemical  ferments  and  have  the  power  of 
changing  other  substances  without  themselves  under- 
going appreciable  change.  Methods  of  ascertaining 
their  presence  in  milk  are  given  later  (pp.  158-163). 

Amounts  of  casein  and  albumin  in  milk. — In  single 
milkings  of  individual  cows,  the  casein  and  albumin, 
taken  together,  vary  from  2.5  to  6  per  cent,  and 
average  about  3.2  per  cent.  Milk-casein  varies  in 
amount  from  2  to  4  per  cent,  and  averages  about  2.5 
per  cent.  Albumin  varies  from  0.5  to  0.9  per  cent, 
and  averages  about  0.7  per  cent.  The  amount  of  ca- 
sein in  relation  to  albumin  varies  greatly.  On  an 
average,  milk  contains  about  3.6  parts  of  casein  for 
-one  of  albumin,  or,  stated  another  way,  casein  forms 
about  80  per  cent,  of  the  nitrogen  compounds  of  milk. 

The  amount  of  casein  and  albumin  in  milk  is  influ- 
enced by  many  conditions,  such  as  influence  the  gen- 
eral composition  of  the  milk,  among  which  are  individ- 
uality, breed,  advance  of  lactation,  etc.  As  the  lacta- 
tion period  advances,  there  is  a  general  tendency  on 
the  part  of  casein  and  albumin  in  milk  to  increase. 

Relation  of  fat  and  nitrogen  compounds  in  milk. — 
In  normal  milk  containing  over  3  per  cent,  of  fat,  the 
amount  of  casein  and  albumin  is  rarely  greater  than 
the  amount  of  fat,  especially  in  the  milk  of  herds  of 
cows.  When  the  per  cent,  of  fat  is  less  than  that  of 
the  nitrogen  compounds,  the  milk  may  generally  be 
regarded  as  skimmed,  especially  in  the  case  of  milk 
from  herds. 


CHEMISTRY   OF   COWS     MILK  13 

MILK-SUGAR 

Milk-sugar,  also  called  lactose,  is  present  in  cows' 
milk  in  solution.  In  general  composition,  it  resembles 
ordinary  sugar,  but  it  is  less  sweet  and  less  soluble 
in  water.  The  amount  of  sugar  in  milk  varies  from 
below  4  to  over  6  per  cent,  and  averages  about  5  per 
cent.  Its  importance  in  dairy  work,  especially  in  con- 
nection with  the  manufacture  of  butter  and  cheesefc 
comes  from  the  ease  with  which  it  is  converted  into 
lactic  acid  by  certain  forms  of  bacteria.  In  the  ordi- 
nary souring  of  milk,  the  amount  of  milk-sugar  de* 
creases  somewhat  more  than  one- fourth  and  there  i& 
formed  as  a  maximum  about  0.9  per  cent,  of  lactic 
acid.  More  acid  may  be  formed  after  some  time. 
Hence,  sour  milk,  when  two  or  three  days  old,  con- 
tains only  3.5  to  4  per  cent,  of  milk-sugar.  The  sugar 
of  milk  passes  largely  into  the  whey  in  cheese-making 
and  forms  over  70  per  cent,  of  the  solids  in  whey. 
The  milk-sugar  of  commerce  is  usually  prepared  by 
evaporating  whey  and  purifying  the  impure  product 
first  obtained. 

THE  SALTS  OF  MILK 

The  salts  of  milk,  -commonly  included  under  the 
term  "ash,"  are  present  in  only  small  amounts,  0.7 
per  cent,  on  the  average;  but  they  have  important 
relations  to  milk  and  its  products.  Our  knowledge  of 
these  compounds  is  very  incomplete.  The  salts  of  milk 
are  commonly  spoken  of  as  the  ash  or  mineral  constitu- 
ents. This  conception  is  somewhat  misleading,  be- 
cause the  materials  appearing  in  the  ash  of  milk  are, 
to  some  considerable  extent,  combined  in  organic  com- 
pounds, instead  of  existing  in  the  milk  as  separate 


14  MODERN    METHODS   OF   TESTING    MILK 

inorganic  bodies.  The  ash  represents  in  amount, 
therefore,  more  than  the  so-called  mineral  constitu- 
ents of  milk  and  less  than  the  salts  of  milk.  While 
the  ash  in  milk  amounts  to  about  0.7  per  cent.,  the 
amount  of  salts  probably  approximates  0.9  per  cent. 
A  portion  of  the  salts  of  milk  is  in  solution,  including 
such  compounds  as  calcium  citrate,  sodium  chloride, 
potassium  acid  phosphate,  etc.,  while  a  portion  (tri- 
calcium  phosphate)  appears  to  be  in  suspension  in 
the  form  of  very  finely  divided  particles. 

THE  GASES  OF  MILK 

Milk  contains  more  or  less  oxygen  and  nitrogen, 
these  gases  being  carried  into  it  mechanically  from 
the  air  in  the  process  of  milking.  It  contains  also, 
when  freshly  drawn,  carbon  dioxide,  already  present 
in  the  udder  milk,  there  being  probably  between  3  and 
4.  per  cent,  by  volume,  a  portion  of  which  escapes  at 
once  while  being  drawn  from  the  udder  under  usual 
conditions. 

GENERAL  SUMMARY 

Milk  contains  water,  fat,  casein,  albumin,  sugar, 
salts,  carbon  dioxide  and  some  other  constituents  in 
small  quantities.  The  fat  and  casein  and  some  of  the 
salts  are  in  suspension  and  not  in  solution,  while  al- 
bumin, sugar  and  the  larger  portion  of  the  salts  are 
held  in  solution  by  the  water. 

As  a  matter  of  convenience,  the  compounds  of  milk 
are  divided  into  certain  arbitrary  groups.  By  one 
system  of  division,  the  compounds  of  milk  are  ar- 
ranged in  two  classes: — (i)  Water,  and  (2)  milk- 
solids  (or  total  solids),  this  second  class  including 


CHEMISTRY   OF   COWS     MILK 


fat,  casein,  albumin,  sugar,  salts  (ash),  etc.  Another 
division  is  made  on  the  basis  of  the  milk- fat  into  (i) 
fat  and  (2)  milk-serum,  which  includes  all  the  milk 
constituents  except  the  fat.  Separator  skim-milk  is 
nearly  pure  milk-serum.  Then  we  have  the  milk- 
solids  subdivided  into  (i)  fat  and  (2)  solids-not-fat 
(casein,  albumin,  sugar,  salts  (ash),  etc.) 

The  following  arrangement  shows  the  general  rela- 
tion of  the  compounds  contained  in  milk,  the  figures 
indicating  the  percentages  present  in  average  milk; 


MILK. 


f  Water 

87.1 

!Fat 
3.9 

Nitrogen 
compounds 

0   Q 

{Casein, 
2.5 
Albumin,  etc 

o.Z 

n  7 

Solids  < 

Solids-not-fat 

u.  / 

12.9 

9.0 

Milk-sugar 

5.1 

I 

Ash  (salts) 

0.7 

f  Carbon  dioxide 
Gases -j  Nitrogen 
(  Oxygen 

AVERAGE  ANALYSIS  OF  COWS'  MILK 


WATER 

TOTAL, 
SOLIDS 

FAT 

CASEIN 

ALBU- 
MIN 

SUGAR 

ASH 

Per  cl. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ci, 

Average  of  5,552 

American  an- 

alyses   c  o  in- 
piled    by   the 

author  

87.1 

12.9 

3.9 

2.5 

0.7 

5.1 

0.7 

Average  cheese- 

factory  milk 

for  the  season 

(May  to  Nov.) 
in  N.Y.  State... 

87.4 

12.6 

3.75 

2.45 

0.7 

5.0 

0.7 

l6  MODERN    METHODS   OF   TESTING   MILK 

REPRESENTATIVE  ANALYSES  OF  PRODUCTS  AND  BY-PRODUCTS  OF  MILK 


WATER 

TOTAL 
SOLIDS 

FAT 

CASEIN 

ALBU- 
MIN 

SUGAR 

ASH 

Butter  

Per  ct. 
15.0 

Per  ct. 
85  0 

Per  ct. 
81  0 

Per  ct. 

1.0 

Per  ct. 

Per  ct. 

Per  ct. 

3.0 

Cheddar  Cheese 
(green) 
Skim-milk 
(separator) 

"Whey  

36.8 
90.3 
93  4 

63.2 
9.7 
6  6 

33.75 

0.10 
0  35 

23.7S2 
2.75 
0  10 

0.80 
0  75 

5.25 

4  80 

5.7s 
0.80 
0  60 

Buttermilk  

90  6 

9  4 

0  10 

2  80 

0  80 

4  40* 

0  70 

1  Salt.    2  Paracasein.    3  Salt  and  Ash.    *  .60  per  cent,  lactic  acid  in  addition. 

DEFINITIONS  AND   STANDARDS   OF  MILK  AND 
MILK    PRODUCTS 

The  United  States  Department  of  Agriculture  has 
established  official  standards  for  purity  of  dairy  and 
other  food  products,  defining  also  what  is  meant  by  the 
terms  used  in  designating  different  materials.  These 
definitions  and  standards  have  been  most  carefully 
worked  out  by  members  of  the  Association  of  Official 
Agricultural  Chemists,  several  years  having  been  de- 
voted to  the  collection  of  data.  The  official  definitions 
and  standards  relating  to  milk  and  milk  products  are 

as  follows: 

A.     MILKS. 

I.  Milk  is  the  fresh,  clean,  lacteal  secretion  ob- 
tained by  complete  milking  of  one  or  more  healthy 
cows,  properly  fed  and  kept,  excluding  that  obtained 
within  15  days  before  and  10  after  calving,  and  con- 
tains not  less  than  8.5  per  cent,  of  solids-not-fat,  and 
not  less  than  3.25  per  cent,  of  milk-fat. 


CHEMISTRY    OF    COWS'    MILK  I? 

2.  Blended  milk  is  milk  modified  in  its  composition 
so  as  to  have  a  definite  and  stated  percentage  of  one 
or  more  of  its  constituents. 

3.  Skim-milk  is  milk  from  which  a  part  or  all  of 
the  cream  has  been  removed  and  contains  not  less 
than  9.25  per  cent,  of  milk-solids. 

4.  Pasteurized  milk  is  milk  that  has  been  heated 
below  boiling,  but  sufficiently  to  kill  most  of  the  active 
organisms  present,  and  immediately  cooled  to  50°  F. 
or  lower. 

5.  Sterilized  milk  is  milk  that  has  been  heated  at 
the  temperature   of   boiling   water   or   higher   for   a 
length  of  time  sufficient  to  kill  all  organisms  present. 

6.  Condensed  milk,  evaporated  milk,  is  fresh,  pure, 
normal  milk   from  which  a  considerable  portion  of 
water  has  been  evaporated  and  contains  such  percent- 
ages of  total  solids  and  of  fat  that  the  sum  of  the  two 
shall  not  be  less  than  34.3  and  the  percentage  of  fat 
shall  not  be  less  than  7.8. 

7.  Sweetened  condensed  milk  is  milk  from  which  a 
considerable  portion  of  water  has  been  evaporated  and 
to  which  sugar  (sucrose)  has  been  added,  and  con- 
tains  not  less  than   28  per  cent,   of  milk-solids,   of 
which  not  less  than  27.5  per  cent,  is  milk-fat. 

8.  Condensed  skim-milk  is  skim-milk  from  which 
a  considerable  portion  of  water  has  been  evaporated. 

9.  Buttermilk   is   the   product   that    remains    when 
butter  is  removed  from  milk  or  cream  in  the  process 
of  churning. 

10.  Goat's  milk,  ewe's  milk,  etc.,  are  the  fresh,  clean, 
lacteal  secretions  free  from  colostrum,  obtained  by  the 
complete  milking  of  healthy  animals  other  than  cows, 


l8  MODERN    METHODS    OF    TESTING    MILK 

properly  fed  and  kept,  and  conform  in  name  to  the 
species  of  animal  from  which  they  are  obtained. 

B.     CREAM. 

1.  Cream  is  that  portion  of  milk,  rich  in  milk- fat, 
which  rises  to  the  surface  of  milk  on  standing,  or  is 
separated  from  it  by  centrifugal  force,  is  fresh  and 
clean  and  contains  not  less  than  18  per  cent,  of  milk- 
fat. 

2.  Evaporated  cream,  clotted  cream,  is  cream  from 
which  a  considerable  portion  of  water  has  been  evap- 
orated. 

C.     MILK-FAT  OR  BUTTER-FAT. 
I.  Milk-fat  or  butter-fat  is  the  fat  of  milk  and  has 
Reichert-Meissl  number  not  less  than  24  and  a  specific 
gravity  of  not  less  than  0.905  (4O°C). 

D.     BUTTER. 

1.  Butter  is  the  clean,  non-rancid  product  made  by 
gathering  in  any  manner  the  fat  of  fresh  or  ripened 
milk  or  cream  into  a  mass,  which  also  contains  a  small 
portion  of  the  other  milk  constituents,  with  or  without 
salt,  and  contains  not  less  than  82.5  per  cent,  of  milk- 
fat.     By  acts  of  Congress  approved  August  2,  1886, 
and  May  9,  1902,  butter  may  also  contain  added  color- 
ing-matter. 

2.  Renovated  butter,  process  butter,  is  the  product 
made  by  melting  butter  and  reworking,  without  the 
addition  or  use  of  chemicals  or  any  substance  except 
milk,  cream,  or  salt,  and  contains  not  more  than  16 
per  cent,  of  water  and  at  least  82.5  per  cent  of  milk- 
fat. 


CHEMISTRY    OF    COWS     MILK  19 

E.     CHEESE. 

1.  Cheese  is  the  sound,  solid,  and  ripened  product 
made  from  milk  or  cream  by  coagulating  the  casein 
thereof  with  rennet  or  lactic  acid,  with  or  without  the 
addition  of  ripening  ferments  and  seasoning,  and  con- 
tains, in  the  water- free  substance,  not  less  than  50  per 
cent,  of  milk- fat.     By  act  of  Congress,  June  6,  1896, 
cheese  may  also  contain  added  coloring  matter. 

2.  Skim-milk  cheese  is  the  sound,  solid  and  ripened 
product  made  from  skim-milk  by  coagulating  the  ca- 
sein thereof  with  rennet  or  lactic  acid,  with  or  without 
the  addition  of  ripening  ferments  and  seasoning. 

3.  Goafs-milk  cheese,  cive's-milk  cheese,  etc.,  are 
the  sound,  ripened  products  made  from  the  milks  of 
the  animals  specified,  by  coagulating  the  casein  thereof 
with  rennet  or  lactic  acid,  with  or  without  the  addi- 
tion of  ripening  ferments  and  seasoning. 

F.     ICE-CREAMS. 

I.  Ice-cream  is  a  frozen  product  made  from  cream 
and  sugar,  with  or  without  a  natural  flavoring,  and 
contains  not  less  than  14  per  cent,  of  milk-fat. 

(2)  Fruit  Ice-cream  is  a  frozen  product  made  from 
cream,  sugar,  and  sound,  clean,  mature  fruits,  and  con- 
tains not  less  than  12  per  cent,  of  milk-fat. 

3.  Nut  ice-cream  is  a  frozen  product  made  from 
cream,  sugar,  and  sound,  non-rancid  nuts,  and  con- 
tains not  less  than  12  per  cent,  of  milk-fat. 

G.     MISCELLANEOUS  MILK  PRODUCTS. 

1.  Whey  is  the  product  remaining  after  the  removal 
of  fat  and  casein  from  milk  in  cheese-making. 

2.  Kumiss  is   the   product  made   by  the   alcoholic 
fermentation  of  mare's  or  cow's  milk. 


CHAPTER   II 

Methods  of  Sampling  and  Preserving  Milk 

Too  much  emphasis  can  not  be  placed  upon  the  im- 
portance of  taking  for  analysis  a  sample  of  milk  that 
truly  represents  the  whole  body  of  milk  from  which 
the  sample  is  taken.  This  statement  applies  equally 
to  any  product  or  by-product  of  milk  that  is  to  be 
tested.  Before  a  sample  for  testing  is  taken,  the  body 
of  milk  from  which  the  sample  is  to  be  drawn  should 
be  uniform  throughout  in  composition.  Several  con- 
ditions may  disturb  the  desired  uniformity  of  compo- 
sition of  a  mass  of  milk,  among  which  are  the  fol- 
lowing : 

(1)  Separation  of  fat. 

(2)  Partial  churning  of  fat. 

(3)  Freezing  of  milk. 

(4)  Souring  of  milk. 

SAMPLING  MILK  WHEN   FAT  HAS   SEPARATED 

The  rapidity  with  which  fat-globules  rise  to  the 
surface  of  milk  in  the  form  of  cream  is  well  known. 
Therefore,  milk  standing  at  rest  soon  loses  its  uni- 
formity of  composition,  the  upper  layers  containing 
more  fat  than  the  lower  ones.  On  this  account  it  is 
always  necessary,  just  before  taking  a  sample  of 
milk  for  testing,  to  make  sure  that  the  body  of  milk 
to  be  tested  has  an  even  composition  throughout. 

Milk  in  which  fat  separation  is  slight. — In  milk 

20 


METHODS   OF   SAMPLING    MILK  21 

in  which  there  is  no  visible  separation  of  cream,  even- 
ness of  mixing  may  be  best  effected  by  pouring  the 
milk  from  one  vessel  to  another  several  times  immedi- 
ately before  each  sample  is  drawn  for  testing.  Stir- 
ring milk,  as  with  a  dipper,  is  less  effective  than 
pouring. 

Milk  in  which  fat  separation  is  marked. — In  milk 
in  which  the  cream  has  separated  in  a  visible  layer, 
the  pouring  needs  to  be  done  a  greater  number  of 
times  than  in  cases  where  the  separation  of  cream  is 
not  noticeable ;  and,  in  order  to  prevent  possible  churn- 
ing of  particles  of  cream,  the  agitation  should  be  as 
gentle  as  may  be  consistent  with  thorough  mixing. 

Milk  containing  dried  cream. — In  cases  where  the 
cream  is  somewhat  dried  or  hardened,  the  milk  should 
be  warmed  to  105°  or  110°  F.  for  5  or  10  minutes 
to  allow  the  cream  to  melt.  The  milk  is  then  vigor- 
ously agitated  and  immediately  sampled. 

SAMPLING  MILK  WHEN  FAT  IS  PARTIALLY 
CHURNED 

Milk- fat  may  separate  from  milk  in  the  form  of 
small  butter-granules,  as  (i)  when  the  mixing  or 
shaking  of  the  sample  to  be  tested  is  done  too  vio- 
lently; (2)  when  milk  in  cans  is  excessively  agitated 
in  transportation;  and  (3)  when  bottles,  partly  full 
of  milk,  are  sent  by  mail  or  express.  In  such  partially 
churned  milk  it  is  difficult  to  get  a  representative 
sample,  and  the  results  of  testing  are,  at  best,  only 
approximate,  unless  special  measures  are  resorted  to 
in  sampling. 

Distributing  fat  by  warming. — In  the  case  of  parr 


22  MODERN    METHODS  OF  TESTING   MILK 

tially  churned  milk,  the  fat  may  be  redistributed  in 
the  milk  by  warming  it  to  105°  or  110°  F.  long  enough 
to  melt  the  butter-granules,  after  which  the  sample 
is  vigorously  shaken,  until  the  fat  is  evenly  distributed 
through  the  milk,  and  then  the  sample  is  drawn  at 
once  for  analysis. 

Dissolving  fat  in  ether. — Another  method  of  treat- 
ing partially  churned  milk,  previous  to  sampling,  is 
to  shake  the  milk  with  5  per  cent,  of  its  volume  of 
ether  until  the  fat-granules  are  redissolved  and  then, 
after  further  vigorous  shaking,  to  take  the  sample  at 
once.  In  this  case  it  is  necessary  to  make  a  correc- 
tion by  adding  to  the  results  5  per  cent,  or  one-twenti- 
eth of  the  result  obtained.  For  example,  a  milk, 
treated  with  5  per  cent,  of  ether,  and  giving,  on  test- 
ing, 3  per  cent,  of  fat,  should  have  added  .15  (5  per 
cent,  of  3),  making  the  corrected  result  3.15  per  cent. 
When  ether  is  used,  extra  care  must  be  observed  in 
mixing  the  acid  and  milk,  (see  p.  62)  as  the  heat  de- 
veloped may  cause  the  ether  to  boil  up  out  of  the 
neck  of  the  test-bottle. 

Measures  for  preventing  the  churning  of  fat  in 
milk. — It  is  better  to  prevent  the  churning  of  fat  in 
milk  than  to  be  put  to  the  extra  trouble  required  to 
get  a  good  sample  from  milk  that  has  in  it  fat-granules. 
Cans  of  milk,  when  necessarily  exposed  to  much  mo- 
tion in  transportation,  should  be  made  as  nearly  full 
as  possible.  In  the  case  of  bottles  of  milk  sent  by 
mail  or  express  for  analysis,  the  churning  of  fat  may 
be  prevented  in  the  following  manner:  Fill  the  bot- 
tle full  of  milk  to  overflowing.  Then  push  in  tightly 
a  stopper  of  cork  or  rubber  in  which  has  been  made 


METHODS  OF  SAMPLING   MILK  23 

from  top  to  bottom  a  hole  one-eighth  inch  in  diameter 
or  less.  Finally,  push  a  close-fitting  plug  of  wood  or 
a  glass  rod  into  the  hole  in  the  stopper. 

SAMPLING  FROZEN  MILK 

Frozen  milk  *s  of  very  uneven  composition  in  dif- 
ferent portions  of  its  mass.  The  crystals  of  ice  con- 
tained in  it  consist  largely  of  water,  while  the  liquid 
portion  contains  most  of  the  milk-solids.  In  such 
cases  it  is  necessary  to  melt  the  frozen  portion  by 
warming,  and  then  to  mix  well  by  gentle  pouring 
from  one  vessel  to  another,  after  which  the  sample  is 
at  once  taken  for  testing. 

SAMPLING  MILK  COAGULATED  BY  SOURING 

A  sample  of  thickened,  sour  milk  can  not,  without 
special  treatment,  be  taken  so  as  to  give  reliable  results 
in  fat  determination.  In  ordinary  curdled  milk  the 
percentage  of  fat  remains  unchanged  in  amount,  but 
it  is  not  evenly  distributed  through  the  milk.  In  or- 
der to  overcome  this  difficulty,  the  coagulated  sub- 
stance must  be  dissolved  before  sampling.  This  is 
done  by  adding  to  the  milk  a  strong  solution  of  caus- 
tic soda  or  potash  (lye),  or  strong  ammonia  water, 
to  the  extent  of  5  or  10  per  cent,  of  the  volume  of  the 
milk  used  for  sampling.  The  alkali  is  shaken  with 
the  milk  until  the  mixture  becomes  completely  liquid, 
after  which  the  sample  is  at  once  drawn  for  testing. 
It  is  necessary  to  make  a  correction  by  adding  to  the 
results  5  or  10  per  cent,  of  the  amount  of  fat  found, 
according  to  the  amount  of  alkali  solution  used.  In 
place  of  using  a  solution  of  alkali,  one  can  add,  in 


24  MODERN    METHODS   OF   TESTING   MILK 

small  portions  at  a  time,  finely  powdered  caustic  soda 
or  potash,  allowing  the  milk  to  stand  some  time  after 
each  addition  of  powdered  alkali  and  shaking  vigor- 
ously, the  additions  of  alkali  and  the  agitation  being 
continued  only  until  the  milk  becomes  completely  liquid. 
In  using  the  alkali  in  solid  form,  no  correction  of  re- 
sults needs  to  be  made.  The  alkali  solution  or  tab- 
lets  described  on  page  142  may  be  used.  A  darkening 
of  the  milk  by  alkali  may  occur  without  affecting  the 
results  of  the  test.  In  testing,  caution  must  be  ob- 
served when  adding  sulphuric  acid  (see  p.  60)  to  milk 
in  which  an  alkali  has  been  used,  since  an  unusual  de- 
gree of  heat  is  produced  and  the  contents  of  the  test- 
bottle  may  spurt  out.  The  acid  must  be  added  slowly 
and  mixed  with  the  milk  much  more  deliberately  than 
usual. 

COMPOSITE  SAMPLING  OF  MILK 

Composite  samples  of  milk. — A  mixture  of  daily 
samples  of  milk,  taken  from  day  to  day  for  several 
days  in  succession,  is  known  as  a  composite  sample. 
In  commercial  work  at  creameries,  cheese-factories, 
milk-shipping  stations,  etc.,  where  the  number  of  pa- 
trons is  large,  a  daily  test  of  the  milk  for  its  fat  con- 
tent is  impracticable.  To  obviate  the  great  amount  of 
work  involved  in  making  daily  tests,  a  jar  is  provided 
for  the  milk  of  each  patron  and  in  this  jar  is  placed 
a  sample  of  each  day's  milk,  when  it  is  delivered,  these 
daily  samples  being  mixed  and  allowed  to  accumulate 
for  a  period  of  one  or  two  weeks.  A  determination 
of  fat  in  such  a  composite  sample  gives  the  average 
percentage  of  fat  in  the  milk  for  the  period  covered 


METHODS    OF    SAMPLING    MILK 


by  the  mixture  of  daily  samples.  This  method  has 
been  proved  to  be  as  accurate  as  that  of  testing  each 
sample  daily  by  itself,  but  there  are  several  precau- 
tions to  be  observed  carefully  in  applying  this  method 
in  commercial  practice. 

The  conditions  that  are  necessary  for  success  in 
using  the  method  of  composite  sampling  may  be  con- 
sidered under  the  following  heads :  ( i )  Systematic 


FIG.    I 
COMPOSITE-SAMPLE    JAR 


FIG.    2 
COMPOSITE-SAMPLE  JAR 


preparation,  (2)  methods  of  taking  daily  samples,  (3) 
use  of  preservatives,  (4)  care  of  composite  samples, 
(5)  age  of  composite  samples,  and  (6)  preparation  of 
composite  samples  for  sampling  and  testing. 

Systematic  preparation  for  taking  composite  sam- 
ples.— A  round  glass  jar  or  bottle,  holding  a  pint  or 
quart,  should  be  provided  for  each  patron.  The  forms 
given  in  Figs.  I  and  2  are  suitable,  or  ordinary  Mason 


MODERN    METHODS   OF   TESTING    MILK 


fruit- jars  may  be  used.  Whatever  form  of  composite- 
sample  jar  or  bottle  be  used,  the  stopper  or  cover 
should  fit  perfectly  tight,  so  as  to  prevent  any  possi- 
ble evaporation  of  water  from  the  sample  of  milk, 

and  care  should  be 
taken  to  keep  the 
covers  or  stoppers 
tight.  Each  sam- 
ple-bottle or  jar 
should  be  labeled 
with  a  name  or 
number  easily  iden- 
tifying the  patron 
furnishing  the  milk. 
The  jars  should  be 
arranged  in  definite 
order  on  a  rack 
(Fig.  3).  placed 
conveniently  near  the  point  where  the  milk  is  deliv- 
ered. As  explained  later,  some  preservative  is  used 
in  each  jar. 

Taking  daily  samples  for  composite  samples. — 
Each  day  when, milk  is  delivered,  the  sample  should 
be  taken  immediately  after  the  milk  has  been  poured 
into  the  weighing  can  before  weighing,  and  should 
then  be  placed  at  once  in  the  composite  jar  or  bottle 
prepared  for  it.  Two  methods  of  sampling  are  in 
common  use,  (i)  by  means  of  a  small  dipper,  and  (2) 
by  means  of  a  sampling-tube. 

(i)  Taking  sample  with  dipper. — A  half-ounce  dip- 
per (Fig.  4)  is  used  for  taking  the  sample  from  the 
weigh-can,  as  soon  as  the  milk  is  poured  in.  The 


FIG.    3 — RACK   FOR   COMPOSITE    SAMPLES 


METHODS   OF   SAMPLING    MILK  27 

sample  is  at  once  placed  in  its  proper  jar  or  bottle. 
Providing  the  milk  is  thoroughly  mixed  in  the  weigh- 
can  and  the  quantity  of  milk  delivered  by  a  patron 


1 


FIG.   4 
SAMPLING-DIPPER 


FIG.    5 
SCOVliLL  SAMPLER 


FIG.    6 
EQUITY    SAMPLER 


from  day  to  day  does  not  vary  much,  this  method  of 
sampling  gives  correct  results. 

(2)  Taking  sample  with  sampling-tube. — There  are 
different  types  of  sampling- tubes  (Figs.  5  and  6),  of 
which  the  Scovell  sampler  is  one  of  the  best.  In  this 


28  MODERN    METHODS   OF   TESTING   MILK 

instrument  the  main  tube  is  open  at  both  ends,  the 
lower  end  closely  fitting  into  a  cap  furnished  with 
three  elliptical  openings.  When  the  sampler,  open  at 
the  bottom,  is  let  down  into  a  can  of  milk,  the  liquid 
pours  into  the  openings  and  fills  the  tube  to  the  height 
of  the  milk  in  the  can.  When  the  cap  comes  in  con- 
tact with  the  bottom  of  the  can,  the  tube  slides  down 
and  closes  the  openings,  after  which  the  tube  can  be 
withdrawn  and  its  contents  emptied  into  the  com- 
posite jar. 

The  tube  method  of  sampling  possesses  two  marked 
advantages  over  the  dipper  method:  (i)  It  always 
takes  an  aliquot  portion,  or  uniform  proportion,  of 
the  milk,  representing  a  small  column  of  the  milk 
from  top  to  bottom;  and  (2)  it  provides  a  strictly  rep- 
resentative sample  of  the  milk,  even  when  sampling 
is  delayed,  because  it  takes  a  uniform  amount  from 
each  layer  of  milk,  going  from  top  to  bottom. 

THE   USE   OF   PRESERVATIVES   IN   COMPOSITE 
SAMPLES 

The  successful  use  of  composite  samples  is  made 
possible  only  by  the  presence  of  some  substance  which 
will  keep  the  milk  from  curdling.  Three  preserva- 
tives have  been  found  especially  useful  for  this  pur- 
pose: (i)  Corrosive  sublimate,  (2)  formalin,  and 
(3)  bichromate  of  potash. 

Corrosive  sublimate,  known  chemically  as  mercuric 
chloride,  has  the  advantage  of  being  a  more  powerful 
antiseptic  than  the  other  substances,  much  smaller 
quantities  being  effective  in  keeping  milk  longer,  but 
it  has  the  disadvantage  of  being  a  violent  poison. 


METHODS   OF   SAMPLING   MILK  29 

When  this  is  used  as  a  milk  preservative,  it  is  a  wise 
precaution  to  add  a  little  coloring  matter  to  the  milk 
in  order  to  warn  every  one  of  its  abnormal  character. 
Corrosive  sublimate,  mixed  with  coloring  matter,  is 
put  up  in  convenient  tablet  form  and  has  found  exten- 
sive use  in  preserving  composite  samples.  All  things 
considered,  it  is  probably  the  most  satisfactory  of  the 
preservatives  commonly  employed. 

Formalin  is  a  liquid  containing  about  40  per  cent, 
of  the  chemical  compound  known  as  formaldehyde.  It 
is  *an  effective  antiseptic  and  has  the  advantage  of 
being  in  liquid  form.  One  cubic  centimeter  of  forma- 
lin should  keep  a  pint  or  quart  sample  of  milk  two 
weeks  or  more.  Formalin  possesses  the  disadvantage 
of  so  hardening  the  milk-casein  that  it  is  not  as  readily 
dissolved  by  sulphuric  acid  (see  p.  63)  as  is  the  casein 
of  untreated  milk.  An  excessive  use  of  corrosive  sub- 
limate may  produce  a  similar  hardening  of  casein. 

Bichromate  of  potash,  also  called  potassium  bichro- 
mate, is  extensively  used  in  preserving  samples  of 
milk  for  testing.  It  is  best  to  use  it  in  powdered  form. 
It  has  the  following  advantages :  ( i )  It  is  compara- 
tively inexpensive.  (2)  It  colors  milk  yellow  and  thus 
shows  its  presence.  (3)  It  is  not  a  very  violent  poison, 
though  not  entirely  harmless.  (4)  It  is  efficient  in 
keeping  milk  for  one  or  two  weeks.  However,  it  has 
some  disadvantages  as  a  preservative  of  composite 
samples  of  milk:  (i)  If  too  much  bichromate  is  used, 
the  solution  of  the  casein  in  sulphuric  acid  is  some- 
what difficult  and  the  final  results  of  testing  may  not 
be  clear.  (2)  In  hot  weather,  it  is  often  difficult  to 
keep  samples  without  using  an  excessive  amount  of 


30  MODERN   METHODS  OF  TESTING  MILK 

bichromate.  (3)  Lactic  acid  in  milk  considerably  re- 
duces the  efficiency  of  bichromate  in  preserving  milk, 
(4)  Samples  of  milk  preserved  with  bichromate  are 
apt,  when  exposed  to  light,  to  form  a  tough  skin  on 
the  surface,  which  interferes  with  proper  sampling; 
this  can  be  largely  decreased  by  keeping  samples  in 
bottles  of  amber  or  brown-colored  glass.  (5)  The 
presence  of  bichromate  in  milk  interferes  with  other 
tests,  such  as  acidity,  specific  gravity,  detection  of 
formalin,  enzyms,  freezing-point  and  refractive  index. 
The  amount  of  potassium  bichromate  to  be  used  in 
composite  samples  is  about  8  or  10  grains  for  half  a 
pint  to  a  pint  of  milk.  The  bichromate  is  put  up  for 
sale  in  tablets  of  convenient  size,  ready  for  use  in  pre- 
serving milk  samples.  Bichromate  can  be  satisfactor- 
ily used  even  in  hot  weather,  if  the  samples  are  kept 
in  a  dark,  cool  place  most  of  the  time. 

CARE  OF  COMPOSITE  SAMPLES 

In  caring  for  composite  samples  of  milk  or  cream, 
some  special  precautions  must  be  observed.  ( i )  Com- 
posite sample  jars  must  be  kept  covered  tight  to  pre- 
vent evaporation  of  water,  which  would  result  in  giv- 
ing a  test  for  fat  higher  than  the  correct  amount.  (2) 
They  should  be  kept  in  a  cool  place,  so  that  the  small- 
est possible  amount  of  preservative  will  need  to 
be  used.  (3)  They  should  be  kept  in  the  dark 
most  of  the  time,  since  direct  sunlight  may  cause 
the  formation  of  a  tough  cream,  rendering  difficult 
the  taking  of  a  good  sample  for  testing.  (4)  When 
the  daily  sample  of  milk  is  added  to  the  composite 


METHODS  OF  SAMPLING  MILK  3! 

sample,  the  contents  of  the  jar  should  be  mixed  by 
giving  the  jar  a  gentle,  rotary  motion.  Unless  this 
is  done  regularly  each  day,  the  cream  that  rises  be- 
comes tough,  especially  where  it  is  in  contact  with  the 
sides  of  the  jar,  and  this  condition  makes  it  difficult 
to  get  a  proper  sample  for  testing.  This  daily  mixing 
also  insures  the  complete  solution  and  distribution  of 
the  preservative  through  the  milk,  which  is  an  es- 
sential condition  of  success  in  keeping  samples.  (5) 
If  a  composite  sample  shows  any  dried  or  churned 
cream,  the  sample  should  be  warmed  to  105°  or  110°  F. 
for  some  minutes  and  then  agitated  vigorously  be- 
fore drawing  the  sample  for  testing. 

AGE  OF  COMPOSITE  SAMPLES  WHEN  TESTED 

It  is  advisable  to  make  the  fat-test  in  composite 
samples,  when  they  have  been  accumulating  for  a 
week  or  ten  days.  In  any  case  the  limit  should  be 
placed  at  two  weeks.  The  custom  practised  by  some 
of  testing  composite  samples  only  once  a  month  should 
be  severely  condemned.  When  samples  are  kept  longer 
than  two  weeks,  it  is  more  difficult  to  get  a  perfectly 
reliable  test  for  fat. 

PREPARATION    OF   COMPOSITE    SAMPLES    FOR 
SAMPLING  AND  TESTING 

When  a  composite  sample  is  to  be  tested,  it  is 
treated  like  any  other  sample  previous  to  taking  the 
sample  for  testing,  as  has  already  been  described  in 
the  first  part  of  this  chapter  on  pp.  20-24. 


CHAPTER   III 

The  Babcock  Test— Description  of  Apparatus 
and  Material 

The  Babcock  test  is  a  method  for  ascertaining  the 
amount  of  fat  in  milk  and  milk  products.  It  was  de- 
vised by  S.  M.  Babcock,  Ph.D.,  chief  chemist  of  the 
Wisconsin  Agricultural  Experiment  Station,  and  was 
first  made  public  in  1890.  There  are  in  use,  espe- 
cially in  Europe,  other  tests,  which  are  more  or  less 
imitations  or  modifications  of  the  Babcock  test,  such 
as  the  Gerber  test  or  acid-butyrometer  and  DeLaval's 
butyrometer. 

The  Babcock  test  solved  the  problem  of  a  rapid,  ac- 
curate, inexpensive  and  simple  method  of  testing  milk 
and  milk  products  for  fat,  and  it  has  found  extensive 
application  in  many  lines  of  dairying,  as  may  be  shown 
by  mention  of  the  following  important  results  coming 
from  its  use :  ( i )  The  payment  for  milk  according  to 
its  fat  content  has  been  made  practicable.  (2)  Mak- 
ers of  butter  and  cheese  have  been  able  to  detect  and 
prevent  abnormal  losses  of  fat  in  the  process  of  man- 
ufacture. (3)  It  has  enabled  milk  producers  to  detect 
unprofitable  cows>  thus  furnishing  an  intelligent  guide 
in  improving  their  herds.  (4)  It  has  done  more  than 
any  other  means  to  stop  the.  watering  and  skimming  of 
milk  in  connection  with  creameries  and  cheese- factor- 
ies. (5)  It  has  been  of  great  service  in  scientific  dairy 
investigations  and  has,  in  general,  been  a  source  of 
educational  inspiration. 

32 


THE   BABCOCK   TEST  33 

PRINCIPLES  AT  BASIS  OF  BABCOCK  TEST 

This  method  is  based  on  the  action  of  two  agents : 
(i)  the  action  of  strong  sulphuric  acid  upon  the  con- 
stituents of  milk-serum,  and  (2)  the  action  of  cen- 
trifugal force. 

Action  of  sulphuric  acid  in  Babcock  test. — The  sul- 
phuric acid  used  in  the  Babcock  test  performs,  at  least, 
three  functions,  which  we  will  consider  briefly. 

(1)  Action  on  serum-solids  of  milk. — Strong  sul- 
phuric acid  acts  chemically  and  physically  upon  the 
milk-serum  solids   (casein,  sugar,  albumin  and  salts) 
in  such  a  way  as  to  destroy  that  strong  mechanical,  ad- 
hesive   influence    exerted    by   the    milk-serum    solids, 
which   tends   to   prevent   the    fat-globules    separating 
from  the  form  of  an  emulsion.    When  this  influence  is 
overcome,  the  fat-globules  are  more  free  to  collect  in 
a  mass. 

(2)  Heat  furnished  by  action  of  sulphuric  acid. — • 
The  action  of  sulphuric  acid  upon  the  water  of  milk- 
serum  and  also  upon  the  organic  solids  of  the  serum 
generates  so  much  heat  that  the  fat-globules  easily  lose 
their  individuality  and  run  together,  a  condition  favor- 
ing rapid  separation  of  fat  from  serum. 

(3)  Specific  gravity  of  serum  increased  by  sulphuric 
acid. — The  sulphuric  acid,  being  nearly  twice  as  heavy 
as  milk,  increases  the  difference  in  specific  gravity  be- 
tween the  milk-fat  and  the  liquid  surrounding  it.    The 
milk-fat,  being  much  lighter,  more  readily  rises  to  the 
surface  of  the  heavy  liquid. 

Action  of  centrifugal  force  in  Babcock  test. — The 
action  of  the  sulphuric  acid  having  released  the  milk- 
fat  largely  from  the  form  of  an  emulsion  in  the  milk- 


34 


MODERN    METHODS   OF    TESTING    MILK 


fc 


FIG.    7 

MILK-TESTING 
BOTTLE 


FIG.  7a 

NECK    SHOWING 
TEST-BOTTLE         GRADUATION   OF 
8%   MILK  8%     MILK-TEST 

BOTTLE 


serum,  the  completion  of  the  separation  of  fat  is  ef- 
fected by  centrifugal  force.  When  the  bottles  con- 
taining the  mixture  of  milk  and  acid  are  whirled,  the 
centrifugal  force  acts  more  strongly  upon  the 
heavier  portion,  that  is,  the  mixture  of  acid  and  milk- 


176  c*. 


THE    BABCOCK  TEST  35 

serum.  Hence  this  heavy  mixture  is 
forced  to  the  outside,  which  is  the  bottom 
of  the  bottle,  while  the  much  ligher  fat  is 
forced  to  the  top.  A  small  amount  of  fat 
(.1  to  .2  per  cent.)  remains  unseparated 
under  usual  conditions. 

The  following  apparatus  and  material 
are  used  in  making  the  tests  (i)  Test-bot- 
tles, (2)  pipette  for  measuring  milk,  (3) 
acid-measure,  (4)  tester  or  centrifugal 
machine,  and  (5)  sulphuric  acid, 

TEST-BOTTLES 

The  usual  forms  of  bottle  used  in  test- 
ing milk  are  shown  in  Fig.  7  and  7a.  The 
neck  of  the  bottle  is  marked  with  a  scale 
so  graduated  that  each  small  division  re- 
presents .2  per  cent,  and  five  of  these  divi- 
sions, making  one  large  division,  represent 
I  per  cent.,  when  we  use  17.5  cc.*  or  18 
grams  of  milk.  The  marks  extend  from  o 
to  8  or  10  per  cent.  Why  do  these  divisions 
represent  exact  percentages  by  weight  of 
fat  in  milk,  when  no  weighing  is  done  in 
testing  milk?'  We  use,  in  testing,  17.5  cc.  of 
milk,  which  is  known  to  weigh  almost  ex- 
actly 18  grams.  The  graduated  portion  of 
the  neck  of  the  test-bottle  is  made  to  hold 


FIG.  8  *cc-  '1S  ti16  abbreviation  for  cubic  centimeters 

PIPETTE      (see  p.  273). 


36  MODERN    METHODS    OF    TESTING    MILK 

exactly  2  cc.  between  the  o  and  10  marks.  Since  I  cc. 
of  pure  milk-fat  is  known  to  weigh  .9  gram,  2  cc.  of 
milk-fat,  the  amount  required  to  fill  the  neck  between 
the  o  and  10  marks,  weighs  1.8  (.9x2)  grams,  which 
amount  is  just  10  per  cent,  of  the  18  grams  of  milk 
sample  used  in  testing. 

In  the  form  shown  in  Fig.  7a,  which  is  coming  into 
common  use,  the  scale  is  limited  to  8  per  cent.,  while 
the  smallest  divisions  measure  o.i  per  cent.  (See 
P- 275). 

The  divisions  on  the  neck  of  the  test-bottle  should  be 
accurate  and  uniform;  the  lines  should  run  straight 
across  the  neck  and  not  obliquely.  When  the  marks 
and  numbers  become  indistinct  from  use,  they  can 
be  rendered  clear  by  rubbing  the  scale  over  with  the 
lead  of  a  pencil  or  with  a  cloth  having  on  it  a  little 
printer's  ink  or  black  paint.  When  in  use,  each  bottle 
should  be  numbered  or  labeled  in  a  distinctive  way. 

MILK-MEASURING  PIPETTE 

The  form  of  pipette  in  common  use  is  shown  in  Fig. 
8.  Other  forms  are  shown  in  Figs.  9  and  10.  The 
pipette  should  hold  17.6  cc.  when  filled  to  the  mark. 
Since  about  .1  cc.  of  milk  will  adhere  to  the  inside, 
such  a  pipette  will  furnish  a  sample  amounting  to 
17.5  cc.  of  milk,  which  weighs  about  18  grams,  I  cc. 
of  milk  weighing  about  1.03  grams  on  an  average. 
The  accuracy  of  the  test,  so  far  as  regards  the  amount 
of  sample  taken,  depends  upon  the  exactness  of  the  pi- 
pette in  holding  17.6.  The  mark  on  the  stem  should, 
for  convenience,  be  two  inches  or  more  from  the  up- 


THE    BABCOCK  TEST 


37 


per  end  of  the  pipette.  The  hole  forming  the  outlet 
should  be  of  such  a  size  as  to  allow  the  contents  of  the 
pipette  to  flow  out  in  5  to  8  seconds.  (See  p.  277). 

MEASURE   FOR   ACID 

A  cylinder  of  glass,  like  that  shown  in  Fig.  n, 
with  a  lip  to  pour  from  and  a  single  mark  at 
17.5  cc.,  is  the  form  commonly  used.  Other  forms 
are  shown  in  Figs.  12  and  13.  These  latter 
forms,  made  so  as  to  hold  enough  acid  for  20 


FIG.    9  FIG.   IO 

AUTOMATIC    PIPETTE       WAGNER^S  PIPETTE 


FIG.    II 
ACID- MEASURE 


MODERN    METHODS    OF    TESTING    MILK 


or  more  tests,  are  probably  the  most  convenient  where 
many  samples  are  to  be  tested  at  the  same  time. 


FIG.    12 
ACID-BURETTE    AND    STAND 


FIG.    13 
AUTOMATIC   BURETTE 


THE    CENTRIFUGAL   MACHINE,    OR    TESTER 

The  centrifugal  machine  used  in  the  Babcock  test 
is  commonly  called  the  Babcock  tester.  Various  forms 
have  been  devised,  varying  in  size  from  those  adapted 
for  a  single  duplicate  test  up  to  the  needs  of  large  fac- 
tories. The  designs  of  recent  years  are  much  superior 
to  the  early  forms.  Some  of  the  different  types  are 


,39 


4O  MODERN    METHODS    OF    TESTING    MILK 

represented  in  Figs.  14,  15,  16  and  17.  In  general 
they  all  consist  of  a  revolving  disc  placed  in  a  hori- 
zontal position,  and  provided  with  swinging  pockets, 


FIG.    l6 — SMALL    HAND-TESTER 

in  which  the  test-bottles  are  placed.  When  at  rest, 
the  pockets  hang  down,  permitting  the  bottles  to 
stand  upright.  When  the  disc  is  in  motion  the  pock- 
ets swing  out,  carrying  the  bottles  to  a  horizontal  posi- 
tion, the  necks  of  the  bottles  being  directed  in  toward 
the  center.  The  testers  should  be  made  to  carry  an  even 
number  of  bottles.  The  steam-turbine  tester  is  the 
best  form  of  centrifugal  for  factory  work.  It  has  the 
advantage  of  maintaining  a  uniform  rate  of  speed 
and,  in  addition,  the  contents  of  the  bottles  are  kept 
hot,  and  hot  water  is  supplied.  In  some  forms,  in 
which  the  exhaust  steam  is  not  carried  away  and  in 


THE    BABCOCK  TEST  4! 

which  no  dampers  are  provided  in  the  cover,  the  steam 
testers  may  heat  the  fat  too  high.  For  use  on  farms, 
hand-testers  are  available.  It  is  always  necessary  that 


FIG.    17 — ELECTRIC  CENTRIFUGAL    MACHINE   OF  LATEST   DESIGN   FOB 
USE  IN  BABCOCK  TEST 

Capable  of  unusually  high  speed — safe,  accurate  and  convenient.     Made 
by  International   Instrument   Co.     Cambridge,   Mass. 

the  tester  should  be  securely  fastened  to  a  firm  founda- 
tion and  so  set  that  the  revolving  disc  is  level.  The 
centrifugal  should  run  smoothly,  without  jar  or  trem- 
ble, when  going  at  full  speed. 

,  Estimating  speed  of  centrifugal  tester. — In  ordet 
to  cause  separation  of  the  most  fat  possible,  the  cen^ 
trifugal  disc  must  move  at  a  sufficient  speed.  The  re-- 
quired number  of  revolutions  depends  upon  the  diame- 
ter of  the  disc,  to  the  edge  of  which  the  test-bottles  are 


42  MODERN    METHODS    OF    TESTING    MILK 

attached.    The  smaller  the  wheel,  the  greater  must  be 
the  number  of  revolutions  a  minute. 

Farrington  and  Woll  have  prepared  the  following 
£able,  showing  the  necessary  number  of  revolutions  for 
different  sizes  of  testers: 

DIAMETER  OF                                                    No.  of  revolutions 
WHEEL  IN  INCHES                                               of  disc  per  minute 
10 1074 

12 980 

14 909 

16 848  ' 

18 800 

20 759 

22 724 

24 693 

In  the  case  of  steam-turbine  testers,  they  are,  or 
should  be,  made  to  run  at  the  desired  speed  under  a 
definite  head  of  steam.  These  testers  should  always 
be  provided  with  a  pressure-gage,  and  a  speed-indi- 
cator is  also  desirable. 

In  the  case  of  hand-testers,  the  speed  can  be  ascer- 
tained in  the  following  manner:  Give  the  handle  one 
full  turn  and  count  the  number  of  times  a  given  point 
on  the  disc  goes  round.  Suppose,  for  example,  that 
the  diameter  of  the  disc  is  16  inches  and  that  it  revolves 
14  times  for  one  turn  of  the  handle.  Such  a  disc  ought 
to  revolve  848  times  per  minute  according  to  the  pre- 
ceding table.  The  handle  must  be  turned  around  as 
many  times  a  minute  as  14  is  contained  in  848  in  or- 
der to  attain  the  desired  speed,  which  is  found  to  be 
about  60  times,  or  once  a  second.  Then,  with  watch 
in  hand,  regulate  the  turning  of  the  handle  until  it 


THE    BABCOCK  TEST  43 

is  made  to  turn  60  times  a  minute.  The  proper  speed 
once  attained  should  be  kept  up  during  the  testing  of 
a  sample.  The  efficiency  of  whirling  can  be  further 
tested  by  treating  different  samples  of  the  same  milk 
at  different  rates  of  speed,  the  highest  per  cent,  of 
fat  beyond  which  there  is  no  increase,  showing  the 
right  speed. 

KIND  OF  ACID  USED  IN  BABCOCK  TEST 

The  acid  used  in  the  Babcock  test  is  commercial  sul- 
phuric acid,  commonly  known  as  oil  of  vitriol.  It 
should  not  be  quite  as  strong  as  the  strongest  com- 
mercial acid.  While  the  strong  acid  has  a  specific 
gravity  of  about  1.84,  the  acid  used  in  the  test  should 
be  between  1.82  and  1.83  at  60°  F. 

Effect  of  weak  acid. — If  the  acid  is  weaker  than 
that  indicated  by  specific  gravity  1.82,  there  is  danger 
that  some  of  the  coagulated  casein  may  not  be  com- 
pletely redissolved  and  this,  mixing  with  the  fat, 
makes  the  fat-column  in  the  test-bottle  more  or  less 
pale  and  cloudy,  when  it  should  be  clear  and  usually 
golden  yellow  in  color.  In  addition,  there  is  apt  to 
be  a  collection  of  cloudy  matter  at  the  foot  of  the  fat- 
column,  obscuring  the  line  of  division  and  making 
sharp  reading  difficult.  The  use  of  more  than  17.5  cc. 
of  acid  not  too  weak  may  give  good  results. 

Effect  of  too  strong  acid. — When  the  acid  is  too 
much  above  specific  gravity  1.83,  the  fat-column  is 
dark  in  color.  There  is  a  layer  of  black  material  be- 
low it,  and  the  amount  of  fat  is  difficult  to  read  with 
accuracy.  When  the  acid  is  too  strong,  it  is  possible 
to  secure  accurate  results  by  using  less  than  17.5  cc. 


44 


MODERN    METHODS    OF    TESTING    MILK 


of  acid,  the  exact  quantity  being  determined  by  trying 
different  amounts  of  acid,  until  the  fat-column  obtained 
is  clear  and  yellow.  Strong  acid,  if  allowed  to  stand 
open  to  the  air,  will  in  time  absorb 
enough  moisture  to  reduce  it  to  proper 
strength.  By  far  the  best  plan  is  to 
purchase  the  acid  of  guaranteed  spe- 
cific gravity  1.82  to  1.83,  since  all 
dairy-supply  houses  now  furnish  such 
acid,  and  then  take  pains  to  keep  the 
acid  in  tightly  stoppered  bottles  when 
not  in  use. 

Testing  strength  of  acid.— The 
strength  of  sulphuric  acid  may  be  con- 
veniently tested  by  a  specially  designed 
hydrometer  (Fig  18).  This  instru- 
ment or  acidometer  is  simply  allowed 
to  float  in  the  sulphuric  acid,  which 
must  be  at  60°  F.,  and  the  specific 
gravity  is  read  from  the  scale  where 
it  coincides  with  the  upper  surface  of 
the  liquid,  which  should  be  between 
the  scale-marks  1.82  and  1.83.  No 
acidometer  should  be  used  whose  ac- 
curacy is  not  reliably  guaranteed.  ACID 

Reducing  the  strength  of  strong  acid. — With  the 
aid  of  an  acidometer,  it  is  possible  to  purchase  strong 
sulphuric  acid  and  dilute  it  to  proper  strength.  This 
is  not  advised  for  the  average  worker.  When  this  is 
done,  extreme  caution  must  be  used  in  diluting  the 
acid.  Never  pour  water  into  strong  sulphuric  acid, 
but  always  add  the  acid  to  the  water.  The  amount  of 


FIG.  1 8 

HYDROMETER  FOR 
TESTING  STRENGTH 

OF  SULPHURIC 


THE    BABCOCK  TEST  45 

dilution  depends  upon  the  strength  of  the  acid  used. 
One  should  start  with  a  small  dilution  and  increase 
gradually  until  the  specific  gravity  of  the  acid  becomes 
1.82  to  1.83.  After  diluting  the  acid  with  water,  the 
mixture  becomes  hot,  and  it  is  necessary  to  allow  it 
to  cool  to  60°  F.  before  testing  with  the  acidometer. 

Useful  indications  regarding  strength  of  acid. — 
After  one  has  acquired  some  skill  in  making  the  Bab- 
cock  test,  one  can  readily  tell  whether  the  acid  is  too 
strong  or  too  weak  from  its  action  when  mixed  with 
milk  in  the  test-bottle.  One  bases  his  judgment  on 
the  rapidity  with  which  the  milk-casein  is  coagulated 
and  redissolved,  and  also  upon  the  quickness  with 
which,  and  the  degree  to  which,  the  mixture  of  acid 
and  milk  turns  dark. 

Keeping  acid  from  air. — The  acid  should  be  kept 
in  tightly  stoppered  bottles',  because,  if  exposed  to  air, 
it  absorbs  moisture  and  becomes  too  weak.  The  stop- 
per should  be  glass,  since  a  common  cork  stopper  is 
soon  destroyed  by  the  acid,  and  even  rubber  is  not 
long  satisfactory. 

Care  in  handling  sulphuric  acid. — Strong  sulphuric 
acid  is  extremely  corrosive  and  is  dangerous  to  han- 
dle except  with  care.  In  contact  with  articles  like 
clothing  or  leather,  it  quickly  ruins  them,  while  on 
the  skin  it  causes  serious  burns  in  a  short  time.  If 
sulphuric  acid  gets  upon  one's  skin,  it  should  be  imme- 
diately and  thoroughly  washed  with  an  abundance  of 
water,  and  this  may  be  followed  by  washing  with  di- 
lute ammonia  or  sodium  carbonate.  In  case  acid  gets 
on  the  clothing,  treat  it  first  with  abundance  of  water 
and  then  with  ammonia.  Red  discoloration  on  cloth- 


46  MODERN    METHODS    OF    TESTING    MILK 

ing  caused  by  acid  may  be  remedied  by  treatment  with 
ammonia,  if  not  too  long  delayed.  Acid  on  tables, 
floors,  etc.,  may  be  neutralized  by  treatment  with 
washing  soda  or  other  alkali. 

METHODS  OF  TESTING  ACCURACY  OF 
APPARATUS 

The  correctness  of  the  graduation  of  the  glassware 
used  in  the  Babcock  test  is  a  fundamental  condition  of 
accuracy  in  the  results  obtained.  In  some  States  all 
graduated  glassware  used  in  the  Babcock  test  must 
be  tested  by  the  State  and  found  correct  before  its  use 
is  permitted  in  commercial  operations.  Reliable  deal- 
ers guarantee  the  accuracy  of  their  glassware,  and  it 
is  found  to  be  much  more  reliable  than  formerly.  How- 
ever, it  is  a  safe  precaution  always  to  test  new  appa- 
ratus before  using  it.  Testing  graduated  glassware 
is  known  technically  as  calibration. 

Testing  or  calibrating  bottles. — In  the  case  of 
standard  milk-testing  bottles,  the  error  of  graduation 
should  not  exceed  o.i  per  cent,  at  any  point  of  the 
scale;  in  the  case  of  standard  cream-testing  bottles, 
the  error  at  any  point  in  the  scale  should  not  be  greater 
than  0.5  per  cent. 

The  most  reliable  method  of  testing  the  accuracy  of 
graduated  glassware  requires  an  accurate  analytical 
balance  with  which  to  weigh  out  exact  amounts  of 
mercury  or  water  (p.  278),  but  simpler  and  more  rapid 
methods  are  available  which  are  sufficiently  accurate 
for  practical  purposes.  Among  the  methods  available 
for  common  use  are  the  following :  ( i )  Testing  with 
water,  (2)  use  of  special  tester  or  plunger,  and  (3) 
testing  with  mercury. 


THE    BABCOCK  TEST  47 

(i)  Testing  with  water. — This  is  the  most  satisfac- 
tory method  when  reasonable  accuracy  is  required  and 
when  it  is  desired  to  test  any  point  of  the  graduated 
scale.  The  only  special  piece  of  apparatus  required 
is  a  burette  (Fig.  21)  holding  50  cc.,  accurately  grad- 
uated to  0.05  or  o.i  cc.  A  finely-graduated  pipette 
holding  5  cc.  or  10  cc.  can  be  used  but  is  less  con- 
venient. 

The  water  used  is  tinged  with  ink  or  any  convenient 
colored  solution  to  make  easier  the  reading  of  the 
height  of  the  column  of  water  in  the  neck  of  the  bot- 
tle. Alcohol  can  be  used  but  is  less  desirable  for  some 
reasons. 

In  this  and  other  methods,  the  temperature  should 
be  the  same  for  the  liquid  and  apparatus  used  in  test- 
ing, and  for  the  glassware  tested.  This  is  easily  man- 
aged by  having  everything  at  the  temperature  of  the 
room  in  which  the  testing  is  done. 

In  detail  the  method  is  carried  out  as  follows :  First, 
fill  up  to  the  zero  mark  with  the  colored  water  the 
bottle  to  be  tested.  With  a  strip  or  coil  of  blotting- 
paper  or  filter-paper,  remove  any  drops  of  water  ad- 
hering to  the  inside  of  the  neck.  Then,  from  the 
burette  run  into  the  bottle  any  desired  amount  of  the 
colored  water  and  read  the  point  on  the  graduated 
neck  to  which  the  water  comes.  It  should  read  the 
same  as,  or  within  o.i  per  cent,  of,  the  amount  of 
water  run  out  of  the  burette.  For  example,  in  testing 
an  ordinary  milk-bottle,  the  addition  of  0.2  cc.  of 
water  should  fill  the  neck  to  the  i  per  cent,  point; 
of  0.4  cc.  to  the  2  per  cent,  point;  of  i  cc.  to  the  5 
per  cent  point,  etc.,  up  to  2  cc.  for  the  10  per  cent. 


48  MODERN    METHODS    OF    TESTING    MILK 

point.  It  is  often  the  custom  simply  to  test  the  scale 
as  a  whole,  running  in  2  cc.  of  water  at  once,  in  which 
case  the  upper  surface  of  the  liquid  should  be  on  a 
level  with  the  10  per  cent,  mark,  if  the  graduation  is 
correct;  for  proper  accuracy,  the  water  should  not 
reach  below  or  above  the  mark  more  than  o.i  cc.  It  is 
possible  that  the  results  may  show  the  scale  to  be  ac- 
curate at  the  10  per  cent,  mark  and  yet  be  incorrect 
at  some  point  below.  It  is,  therefore,  desirable  to 
apply  the  test  to  several  different  points  between  the 
zero  and  10  per  cent,  marks. 

In  the  case  of  cream- testing  bottles,  the  same  oper- 
ation is  performed,  but  it  must  be  kept  in  mind  that 
the  relation  of  the  volume  to  per  cent,  marks  is  differ- 
ent in  i8-grarn  bottles  as  compared  with  g-gram  bot- 
tles; each  cubic  centimeter  in  the  graduated  neck  of 
an  1 8-gram  bottle  stands  for  one-half  the  percentage 
that  it  does  in  a  Q-gram  bottle;  or,  stated  in  another 
way,  each  per  cent,  in  an  1 8-gram  bottle  represents 
twice  the  volume  or  number  of  cubic  centimeters  that 
it  does  in  a  g-gram  bottle.  This  is  shown  clearly  in 
the  following  table: 

In  18-gram  bottles  In  9-gram  bottles 

0.05  cc.  equals 0.25  per  cent.          0.50  per  cent. 

o.i     "       "        0.50    "      "  1.00    "      " 

0.2     "      "       1.00   "     "  2.00   "     " 

0.4      "         "          2.00    "       "  4.00    "       " 

0.5   "     "     2.50  "    "         5.00  "    " 

07  "    "     3.50  "    "         7.00  "    " 

1.0      "         "          5.00    "       "  10.00     "       " 

2.0      "         "          10.00    "       "  20.00     "       " 

3.0  "    "     15.00  "  ."       30.00  "    " 

5.0  "    "     ......25.00  "    "       50.00  "    " 


THE    BABCOCK    TEST 


49 


(2)  Testing  with  special  bottle-tester. — The  quick- 
est method  of  testing  the  accuracy  of  the  graduation 
of  a  test-bottle  is  to  use  a  special  device,  which  is  es- 
sentially  a  simple  brass  plun- 
ger (Fig.  19).  This  instru- 
ment  is  divided  into  two  equal 
portions,  each  part  being 
made  of  such  size  as  to  dis- 
place exactly  one  cubic  centi- 
meter of  liquid.  This  bottle- 
tester  is  used  as  follows: 
The  test-bottle  is  filled  to  the 
zero  mark  with  milk,  or  one 
may  use  water  or,  better, 
wood  alcohol,  imparting  color 
to  the  water  or  alcohol  by 
adding  some  black  aniline  or 
carmine  ink.  Fill  the  bottle 
nearly  to  the  zero  mark  and 
then  finish  with  a  pipette  or 
dropper,  adding  a  drop  at  a 
time  just  to  the  mark.  Any 
drops  of  liquid  adhering  to  the 
inside  walls  of  the  neck  must 
be  removed,  using  conven- 
iently a  strip  of  blotting  or 

FIG.    IQ  FIG.  20  ™ 

MILK-BOTTLE     TESTING        nlter    paper.      The    tester    is 
TESTER      ACCURACY  OF    then  slowly  lowered  into  the 

MILK-BOTTLE  ,  -     ^  ,1^1  .-i 

neck  of  the   test-bottle  until 

the  liquid  rises  half  way  between  the  two  sections  of 
the  instrument,  when  the  upper  surface  of  the  liquid 
should  be  at  the  5  per  cent,  mark  (Fig.  20),  if  the  scale 


5O  MODERN    METHODS    OF    TESTING    MILK 

is  correct  to  this  point.  If  the  surface  of  the  liquid  is 
above  or  below  the  5  per  cent,  mark,  then  that  portion 
of  the  scale  is  incorrect  to  extent  shown.  After  the  ac- 
curacy of  the  5  per  cent,  mark  is  tested,  the  instru- 
ment is  then  lowered  into  the  bottle  until  the  liquid 
rises  about  one-eighth  of  an  inch  above  the  top  of 
the  upper  section  of  the  tester.  If  the  upper  surface 
of  the  liquid  is  level  with  the  10  per  cent,  mark,  the 
graduation  is  correct  at  that  point.  The  graduation 
of  the  scale  is  supposed  to  be  correct,  if  the  tester 
shows  the  5  and  10  per  cent,  marks  to  be  correct. 

In  explanation  of  the  use  of  this  form  of  bottle-tes- 
ter, it  is  to  be  remembered  that  the  neck  of  the  milk- 
bottle  is  so  graduated  as  to  hold  2  cc.  between  the  o 
and  10  marks;  hence,  the  volume  between  the  o  and 
5  marks  should  be  I  cc.,  and  that  between  the  5  and 
10  marks  should  be  also  i  cc.  The  brass  plunger  is 
so  made  that  each  section  displaces,  or  forces  up  into 
the  neck,  i  cc.  of  liquid,  the  whole  instrument  displac- 
ing 2  cc.  This  tester,  therefore,  gives  two  tests  of  the 
scale,  one  at  the  5  per  cent,  mark  and  the  other  at 
the  10  mark,  but  does  not  show  the  accuracy  for  .any 
other  point. 

Some  of  these  instruments  are  made  to  test  the  4 
and  8  per  cent,  points,  so  that  with  two  testers,  one 
can,  if  desired,  test  the  accuracy  of  the  scale  at  the 
4,  5,  8  and  10  points. 

In  using  this  bottle-tester  the  following  precautions 
are  to  be  observed: 

(i)  Have  the  upper  surface  of  the  liquid  exactly 
on  a  level  with  the  zero  mark  in  the  neck  of  the  test- 
bottle  before  putting  the  tester  in. 


THE    BABCOCK    TEST  SI 

(2)  Clean  the  inside  walls  of  the  neck  of  the  bot- 
tle from  adhering  liquid  before  testing, 

(3)  No  air-bubbles  should  be  allowed  to  adhere  to 
the  tester  when  it  is  below  the  liquid. 

(4)  The  tester  should  be  dry  each  time  before  using. 

(5)  The  temperature  of  the  instrument,  liquid  and 
bottle  tested  should  be  the  same. 

(6)  While  making  the  test,  do  not  hold  the  bottle 
in  the  hand,  because  the  heat  of  the  hand  will  produce 
expansion  in  the  liquid  and  thus  make  the  results  in- 
correct. 

Testers  of  the  same  form  are  made  for  cream-bot- 
tles. Some  difficulties  are  met  in  their  use.  In  test- 
ing bulb-necked  bottles,  the  plunger  does  not  enable 
one  to  learn  whether  the  bulb  itself  has  the  exact  ca- 
pacity it  should.  The  wire  which  forms  a  part  of  the 
instrument  may  interfere  with  the  correct  reading  of 
the  meniscus.  In  cream-bottles  with  narrow  necks, 
it  has  been  found  necessary  to  have  the  first  addition 
of  water  reach  one-half  of  the  meniscus  above  the 
zero  mark  in  order  to  bring  the  bottom  of  the  menis- 
cus in  the  top  of  the  neck  on  a  level  with  the  highest 
mark  of  graduation,  after  the  plunger  is  inserted.  In 
the  case  of  wide-necked  bottles,  the  water  should  be 
run  into  the  bottle  at  the  start  so  that  the  meniscus  is 
on  a  level  with  the  zero  mark,  which  then  brings  the 
bottom  of  the  meniscus  at  the  top  of  the  neck  on  a 
level  with  the  highest  mark  of  graduation,  after  the 
plunger  is  inserted. 

(3)  Testing  with  mercury. — From  an  accurately 
graduated  burette  measure  2  cc.  of  clean  mercury 
into  the  bottle  to  be  tested.  Then  push  down  into 


52  MODERN    METHODS    OF    TESTING    MILK 

the  neck  of  the  bottle  as  far  as  the  top  line  of  grad- 
uation a  close-fitting  cork  or  plug,  cut  off  square  at 
the  lower  end.  Turn  the  bottle  upside  down,  caus- 
ing the  mercury  to  run  into  the  neck.  The  mercury 
just  fills  the  space  in  the  neck  between  the  o  and  10 
mark,  if  the  graduation  is  accurate.  The 
same  mercury  can  be  used  in  the  same  way  in 
testing  one  bottle  after  another 
by  transferring  all  the  mercury 
from  one  bottle  to  another, 
which  may  be  conveniently  done 
by  slipping  a  piece  of  elastic, 
rubber  tubing  over  the  ends  of 
the  necks  of  the  two  bottles. 
In  using  the  same  mercury  for 
testing  one  bottle  after  another, 
no  mercury  must  be  lost  in 
transferring,  and  none  must  be 
left  in  the  bottle  last  tested. 
FIG.  21  The  inside  walls  of  the  test-bot- 

BURETTE    AND    SUPPORT    ., 


order  to  prevent  any  mercury  adhering.  (See  p.  278). 
Testing  accuracy  of  pipette. — When  many  pipettes 
are  to  be  tested,  one  runs  into  one  pipette  from  an 
accurately  graduated  burette  (Fig.  21),  17.6  cc.  of 
mercury,  closing  the  lower  end  of  the  pipette.  The 
mercury  should  fill  the  pipette  just  to  the  17.6  cc. 
mark,  if  the  mark  is  correct.  The  same  mercury  can 
be  transferred  to  other  pipettes  in  succession.  Care 
must  be  taken  to  have  the  pipettes  clean  and  dry  in- 
side and  that  all  the  mercury  is  transferred  without 
loss. 


THE    BABCOCK    TEST  53 

When  only  one  or  a  few  pipettes  need  testing, 
water  can  be  used,  running  from  a  burette  into  each 
pipette  17.6  cc.  of  water,  which  should  just  fill  the 
pipette  to  the  mark,  if  accurate.  (See  p.  278). 

Testing  accuracy  of  acid  measure.  —  Ordinarily  the 
acid  measure  does  not  need  testing,  since  a  little  varia- 
tion does  not  affect  the  results.  When  desired,  it  can 
be  tested  by  running  in  water  or  milk  from  a  17.6  cc. 
pipette,  known  to  be  accurate. 

KEEPING  GLASSWARE  CLEAN 

It  is  very  important  that  the  test-bottles  and  the 
pipettes  used  in  the  Babcock  test  should  be  kept  as 
clean  as  possible  from  fat  adhering  to  the  inside  sur- 
face. Unless  a  special  effort  is  made,  the  bottles 
quickly  become  covered  inside  with  a  film  of  fat, 
which  may  be  sufficient  to  increase  appreciably  the 
results  obtained  when  the  bottles  are  used  in  testing. 
The  bottles  should  be  kept  entirely  free  from  any  fat- 
film  and  the  wall  should  be  clear 
and  bright.  This  can  be  accom- 
plished without  serious  trouble. 

As  soon  as  a  test  is  completed 
and  the  amount  of  fat  read,  the 
test-bottle,  while  still  warm,  should 
be  emptied.  This'  may  easily  be 


. 

TEST-BOTTLES         ware   jar  or   crock,   covered    with 

a  board   (Fig.  22),   in  which  are 

several  holes  large  enough  to  admit  easily  the  necks 

of  test-bottles.     The  bottle  is  inverted,  the  neck  run 

down  through  one  of  these  holes,  and  at  the  same  time 


54 


MODERN    METHODS    OF    TESTING    MILK 


FIG.    23 — TEST-BOTTLE    RINSER 

the  bottle  is  shaken  up  and  down  in  order  to  remove 
the  white  calcium  sulphate  deposited  on  the  bottom 
of  the  bottle  during  the  test.  Then,  when  one  is  ready 
to  clean  up  all  the  bottles  that  have  been  used,  each 
one  is  rinsed  with  8  or  10  cc.  of  a  solution,  consisting 
of  one  ounce  of  potassium  bichromate  dissolved  in 


FIG.   24 — TEST-BOTTLE  DRAINING-RACK 

one  pint  of  sulphuric  acid.  Then  a  test-bottle  brush 
is  run  once  up  and  down  the  neck  of  each  bottle,  and 
finally  each  is  well  rinsed  with  hot  water. 


THE    BABCOCK    TEST 


55 


There  are  available  several  devices  which  may  be 
found  convenient  and  time-saving  where  many  bottles 
are  used  daily.  Among  these  devices  may  be  men- 
tioned a  bottle-rinser  (Fig.  23),  a  drain-rack  (Fig. 
24),  and  a  bottle-washer  (Figs.  2$a,  b,  and  c),  des- 
cribed by  Farrington  (Bulletin  129,  Wis.  Agr.  Exp. 
Station,  pp.  22-24). 


FIG.    250 — BOTTLE-HOLDER,   EMPTY 


CHAPTER   IV 


Method  of  Operating  the  Babcock  Test 

In  describing  the  method  of  operating  the  Babcock 
test,  when  determining  the  amount  of  fat  in  milk, 
special  attention  will  be  called  at  each  step  to  such 
difficulties  as  may  occur,  and  emphasis  will  be  placed 
upon  such  precautions  as  experience  has  shown  to  be 
necessary  in  order  to  obtain  accurate  results-. 

In  brief  outline,  the  different  steps  may  be  stated 
as  follows: 

I  Mix  thoroughly  sample  of  milk,  which   is  at  60°   to 
;o°F. 

2.  Quickly  fill  pipette  to  mark  with  milk. 

3.  Run  milk  into  test-bottle. 

4.  Fill  acid-measure  to  mark  with  acid  and  pour  into 

test-bottle. 

5.  (i)   Mix  milk  and  acid  thoroughly  by  rotary  motion; 

(2)   let  stand  2  to  5  minutes;  and  (3)  mix  again. 

6.  Put  test-bottles  in  tester  (centrifuge)  and  whirl  4  or 

5  minutes  at  proper  speed. 

7.  (i)  Add  fairly  hot  water  up  to  neck  of  bottles;    (2) 

whirl  one  minute;  (3)  add  hot  water  to  8  or  9  per 
cent,  mark;  and  (4)   whirl  one  minute. 

8.  Read  results  at  temperature  of  about  130°  F. 

PREPARING  SAMPLES   OF   MILK   FOR  TESTING 

The  milk,  which  should  be  at  a  temperature  of  60° 
to  70°  F.,  is  thoroughly  mixed  by  pouring  from  one 
vessel  to  another  two  or  three  times,  at  least,  imme- 

57 


,58  MODERN    METHODS   OF  TESTING   MILK 

diately  before  taking  the  sample  for  testing.  The  spe- 
cial methods  of  preparing  milk  for  sampling  under 
various  conditions  are  fully  considered  in  Chap.  II, 
p.  20.  The  fat  must  be  evenly  distributed  through 
the  milk  just  before  sampling. 

Every  sample  of  milk  should  always  be  tested  in 
duplicate,  that  is,  two  tests  should  be  made  at  the 
same  time.  This  insures  greater  accuracy.  If  the 
results  of  the  duplicate  test  do  not  agree,  there  is  an 
error  somewhere  and  the  work  must  be  repeated.  Also, 
in  case  one  test  is  lost  and  another  sample  can  not  be 
obtained,  the  remaining  test  can  be  used,  and  the  whole 
work  will  not  be  lost. 

TAKING  SAMPLES  OF  MILK  WITH  PIPETTE 

The  measuring  pipette  (Fig.  8,  p.  35),  is  filled  at 
once  after  the  thorough  mixing  of  the  milk.  This  is 
done  by  placing  the  lower  end  of  the  pipette  well  down 
in  the  milk  and  sucking  up  the  milk  until  it  reaches 
a  point  in  the  pipette  somewhat  above  the  mark  around 
its  upper  stem.  Then  the  forefinger,  which  must  be 
dry,  is  quickly  placed  over  the  upper  end  of  the  pi- 
pette before  the  milk  runs  down  below  the  mark.  By 
lightening  the  pressure  of  the  finger  on  the  end  of 
the  pipette,  the  milk  is  allowed  to  flow  out  slowly  un- 
til its  upper  surface  just  reaches  the  mark  on  the 
stem.  Some  practice  is  necessary  before  one  can  eas- 
ily and  rapidly  manipulate  the  pipette  with  accuracy. 

The  pipette  must  be  kept  very  clean.  When  sam- 
ples of  several  different  milks  are  to  be  drawn  in  suc- 
cession, the  pipette  may  be  satisfactorily  rinsed  by 


THE    BABCOCK   TEST 


59 


drawing  it  full  of  the  milk 
next  to  be  sampled,  this  por- 
tion being  thrown  away. 

TRANSFERRING  SAMPLE 

OF  MILK  FROM  PIPETTE 

TO  TEST-BOTTLE 

Having  filled  the  pipette 
just  to  the  17.6  cc.  mark,  one 
holds  the  pipette  obliquely  to 
the  bottle,  placing  the  point 
of  its  lower  end  within  the 
neck  and  against  the  side  of 
the  neck  of  the  test-bottle. 
The  right  way  of  holding  the 
pipette  is  shown  in  Fig.  26. 
By  loosening  the  finger  at 
the  upper  end  of  the  pipette, 
one  allows  the  milk  to  flow 
slowly  down  the  inside  of  the  V 
neck.  The  small  portion  of 
milk  adhering  to  the  inside  of • 
the  pipette  is  nearly  all  carried 
into  the  bottle  by  blowing 
through  the  pipette  several 
times  before  removing  it  from 
the  neck  of  the  bottle.  Not 
a  drop  of  the  milk  should  be  FIG.  26 — CORRECT  WAY  OF 
allowed  to  spill  outside  the  HOLDING  PIPETTE  AND 
bottle  in  transferring  from  BOTTLE 

the  pipette. 

It  is  not  intended  to  remove  every  trace  of  milk 
from  the  pipette  into  the  bottle,  since  allowance  for 


6o 


MODERN     METHODS    OF    TESTING    MILK 


what  remains  is  made  in  the 
construction  of  the  pipette. 
Special  experiments  having 
shown  that  .1  cc.  of  milk  will 
remain  adhering  to  the  inside, 
the  pipette  is  made  to  hold 
17.6  cc.  to  the  mark,  but  is 
expected  to  deliver  into  the 
bottle  only  17.5  cc.,  the  exact 
amount  required  for  the  test. 
In  delivering  the  milk,  the 
pipette  must  never  be  held 
perpendicularly  in  a  line  with 
the  neck  of  the  test-bottle, 
running  the  milk  straight 
down  as  shown  in  Fig.  260,, 
since  the  narrow  neck  may 
easily  choke  up  with  milk  and 
run  over  the  top. 

MEASURING  AND  ADDING 
ACID 

When  the  samples  of  milk 
are  in  the  test-bottles,  the  acid- 
measure  (Fig.  n,  p.  37),  is 
filled  to  the  17.5  cc.  mark  and 
the  acid  (see  p.  43)  is  poured 
into  the  test-bottle.  The  acid 
should  be  at  a  temperature  of 
60°  to  70°  F.  Much  care 
must  be  exercised  in  pouring 

the  acid  into  the  test-bottle  containing  the  milk.    The 
test-bottle  is  held  in  an  inclined  position,  so  that  the 


FIG.  26a — WRONG  WAY  OF 

HOLDING   PIPETTE   AND 

BOTTLE 


THE    BABCOCK    TEST  6l 

acid  will  follow  the  inside  wall  down  to  the  bottom, 
and  the  pouring  should  be  slow  and  steady.  Thus 
handled,  the  acid,  being  much  heavier  than  the  milk, 
forms  a  layer  by  itself  at  the  bottom  of  the  bottle, 
while  the  milk  forms  a  separate  layer  by  itself  on  top 
of  the  acid.  While  pouring  in  the  acid,  it  is  well  to 
turn  the  test-bottle  around  slowly  so  that  the  acid  may 
in  turn  come  in  contact  with  different  portions  of  the 
inside  walls  of  the  neck  and  wash  down  any  adhering 
milk.  Unless  this  is  done,  some  milk  may  remain  on 
the  wall  of  the  neck,  in  which  case  it  will  not  be  prop- 
arly  acted  on  by  the  acid,  and  the  fat-column  will  con- 
tain particles  of  undissolved  casein. 

If  one  attempts  to  pour  the  acid  straight  down  the 
neck  of  the  bottle,  two  difficulties  are  liable  to  occur : 
(i)  The  neck  may  easily  choke  up  and  the  acid  over- 
flow on  the  operator's  hands.  (2)  The  acid  may  drop 
into  and  partially  mix  with  the  milk,  in  which  case 
black  particles  may  appear  on  the  upper  surface  of  the 
acid  layer  and  later,  mixing  in  the  fat-column,  may 
interfere  with  accurate  reading  of  the  results. 

Temperature  of  milk  and  acid. — It  is  directed  to 
have  the  milk  and  acid  at  a  temperature  of  60°  to 
70°  F.  before  they  are  placed  in  the  test-bottle.  There 
are  good  reasons  for  this  precaution.  If  the  milk  or 
acid  is  decidedly  cold,  as  may  easily  happen  in  cold 
weather,  the  action  of  the  acid  may  not  be  vigorous 
enough  to  redissolve  completely  the  coagulated  casein, 
thus  producing  white  specks  or  a  cloudy  appearance 
in  and  below  the  fat-column  at  the  end  of  the  test. 
On  the  other  hand,  if  the  milk  or  acid  is  at  too  high 
a  temperature,  as  may  easily  happen  in  hot  weather, 


62  MODERN   METHODS  OF  TESTING   MILK 

the  action  of  the  acid  is  much  the  same  as  if  it  were 
too  strong,  producing  dark-colored  specks  or  a  dark- 
ened appearance  in  and  below  the  fat-column.  Ex- 
perience shows  that  when  the  milk  and  acid  are  at  a 
temperature  between  60°  and  70°  F.,  there  is  no  dan- 
ger of  too  slight  or  too  strong  action  of  acid.  More 
acid  can  be  used  at  lower  temperatures  and  less  at 
higher  temperatures  with  satisfactory  results,  but  this 
involves  experimenting;  the  best  way  will  be  to  use 
the  regular  amount  of  acid  and  regulate  the  tempera- 
ture of  the  milk  and  acid. 

MIXING  MILK  AND  ACID  IN  TEST-BOTTLE 

When  the  measured  amount  of  acid  has  been  placed 
in  the  test-bottle,  the  acid  and  milk  should  be  thor- 
oughly mixed.  This  is  best  done  by  giving  the  bot- 
tle a  rotary  motion,  with  gentle  shaking,  until  the 
whole  mass  becomes  liquid  and  free  from  solid  parti- 
cles of  casein.  Much  motion  up  and  down  should  be 
avoided,  since  milk  might  be  thrown  up  into  the  neck 
of  the  bottle  beyond  reach  of  the  acid,  in  which  case 
coagulated  casein  would  contaminate  the  fat-column 
and  impair  the  results. 

When  the  acid  and  milk  first  mix,  the  casein  is 
coagulated  in  a  somewhat  solid  mass,  which  gradu- 
ally redissolves  as  the  mixing  becomes  complete.  The 
mixing,  once  begun,  should  continue  until  the  casein 
appears  to  be  redissolved.  If  the  operation  of  mixing 
milk  and  acid  is  incomplete  or  is  interrupted,  black 
particles  may  appear  in  the  fat-column  at  the  end  of 
the  test. 

It  is  a  wise  precaution  to  allow  the  bottle  to  stand 


THE    BABCOCK    TEST  63 

2  to  5  minutes  after  the  mixing  appears  complete  and 
then  to  agitate  a  second  time  with  rotary  motion  just 
before  placing  in  the  tester. 

The  action  of  the  sulphuric  acid  upon  the  water  and 
organic  solids  of  the  milk  produces  a  marked  degree 
of  heat,  as  soon  as  the  acid  and  milk  begin  to  mix. 
The  color  of  the  solution  becomes  yellow  at  first  and 
then  passes  through  varying  darker  shades  of  yellow 
to  violet,  brown  and  finally  dark-brown,  if  the  acid  is 
of  the  right  strength.  (See  p.  43).  The  coloration  is  due 
to  the  action  of  the  acid  upon  the  milk-sugar  and  milk- 
casein.  Too  strong  acid  produces  a  dense  black  color. 
In  samples  of  milk  containing  too  much  bechromate  of 
potash,  the  color  becomes  greenish  black. 

Samples  of  milk  that  have  been  preserved  for  some  ' 
time  with  biochromate  or  formalin,  especially  when  the 
preservation  is  used  in  larger  than  usual  amounts,  re- 
quire more  time  and  agitation  to  redissolve  the  coag- 
ulated casein  than  do  ordinary  samples,  since  these 
preservatives  harden  the  coagulated  casein.  (See  p.  29). 

WHIRLING  THE  TEST-BOTTLES 

The  test-bottles  containing  the  mixture  of  milk  and 
acid,  after  being  agitated  a  second  time  as  stated  above, 
are  placed  in  the  centrifugal  tester  (p.  38),  and 
whirled.  This  is  better  done  soon  after  the  milk  and 
acid  are  mixed,  but  it  may  be  delayed  without  harm 
.for  24  hours,  in  which  case,  however,  the  bottles 
should  be  placed  in  water  at  160°  to  180°  F.  for  15 
or  20  minutes  before  whirling. 

An  even  number  of  bottles  should  be  whirled  at  the 


64  MODERN    METHODS  OF  TESTING   MILK 

same  time  and  they  should  be  placed  about  the  disc 
in  pairs  opposite  to  each  other,  so  that  the  equilibrium 
of  the  tester  will  not  be  disturbed.  When  all  the  sam- 
ples to  be  tested  are  placed  in  the  tester,  the  cover 
is  placed  on  the  jacket  and  the  machine  turned  for  4 
or  5  minutes  at  proper  speed,  600  to  1,200  revolutions 
per  minute,  according  to  the  diameter  of  the  centri- 
fugal disc.  (p.  41). 

The  whirling  brings  the  fat  to  the  top  of  the  mix- 
ture in  the  test-bottle.  The  whirling  of  the  bottles 
should  never  be  done  without  having  the  cover  on  the 
jacket,  for  two  reasons:  (i)  The  cover  prevents  the 
cooling  of  the  fat  in  the  test-bottles,  and  (2)  the 
operator  is  protected  from  injury  in  case  a  bottle  should 
break  and  scatter  its  contents  while  being  whirled. 

In  the  case  of  hand-testers,  it  may  be  necessary  to 
put  hot  water  in  the  jacket  in  cold  weather  in  order 
to  keep  the  bottles  warm  enough. 

ADDING  HOT  WATER  TO   THE  TEST  BOTTLES 

When  the  bottles  have  been  whirled  4  or  5  minutes, 
moderately  hot  water  is  added  to  each  bottle  until  the 
contents  come  to  the  lower  end  of  the  neck.  The 
water  may  be  added  with  a  pipette  or  by  means  of 
any  convenient  arrangement.  The  cover  of  the  ma- 
chine is  replaced  and  the  bottles  are  whirled  at  full 
speed  for  one  minute.  Hot  water  is  again  added  to 
the  bottles  until  the  fat,  which  is  lighter  than  the  rest 
of  the  liquid,  rises  in  the  neck  to  the  8  or  9  per  cent, 
mark.  One  must  be  careful  never  to  raise  the  fat 
above  the  10  per  cent.  mark.  The  whirling  is  then  re- 
peated for  one  minute  at  full  speed. 


THE    BABCOCK  TEST  65 

Three  points  deserve  attention  in  this  connection: 
(i)  The  temperature  of  the  water  added,  (2)  the 
kind  of  water  used  and  (3)  the  number  of  times  water 
is  added. 

(1)  The  temperature  of  the  water  added  should  be 
above  120°  F.   The  aim  in  general  should  be  to  have 
the  temperature  of  the  fat  at  the  close  of  whirling  at 
130°  or  140°   F.,  and  the  temperature  of  the  water 
added  should  have  reference  to  this  fact.     However, 
any  effect  of  too  hot  or  too  cold  water  can  be  remedied 
after  the  final  whirling  by  adjusting  the  temperature 
as  needed. 

(2)  Clean,  pure,  distilled  water  is  the  best  form  to 
use  and,  next,  soft  rain  water.    Hard  water  may  seri- 
ously affect  the  results.     Objections  to  hard  water 
may  in  most  cases  be  overcome  by  thorough  boiling 
or  by  previous  treatment  with  a  few  drops  of  sul- 
phuric acid. 

(3)  Some  operators  add  the  hot  water  only  once, 
filling  the  bottle  to  near  the  top  of  the  neck  immedi- 
ately after  the  first  whirling.     The  advantage  of  ad- 
ding the  water  in  two  portions  is  that  the  fat  is  washed 
free  from  adhering  impurities,  since  the  fat-column  is 
often  mixed  with  various  particles  which  render  the 
reading  uncertain  and  frequently  too  high. 

READING  RESULTS  IN  PERCENTAGE  OF  FAT 

After  the  last  whirling  is  completed,  the  test-bottles 
are  removed  from  the  tester,  one  at  a  time,  in  order 
to  read  the  results  of  the  test.  To  ascertain  the 
amount  of  fat,  hold  the  test-bottle  upright,  having  the 
graduated  scale  of  the  neck  of  the  bottle  on  a  level 


66  MODERN    METHODS   OF  TESTING   MILK 

with  the  eye.  Notice  the  divisions  marking  the  high- 
est and  lowest  limits  of  the  fat-column.  The  differ- 
ence between  them  gives  directly  the  per  cent,  of  fat 
in  the  milk  tested.  The  readings  can  be  made  accu- 
rately to  one-half  of  a  division,  that  is,  to  one-tenth  of 
one  per  cent.  Some  test-bottles  are  provided  with  a 
regulator  which  moves  the  bottom  of  the  fat-column 
to  a  level  with  the  nearest  numbered  mark. 

In  connection  with  the  measuring  of  the  fat-column, 
the  following  points  deserve  attention :  ( i )  Using  divi- 
ders to  assist  in  reading,  (2)  the  temperature  of  the 
fat-column,  (3)  the  upper  and  lower  limits  of  the 
fat-column,  (4)  the  correct  appearance  of  the  fat- 
column,  (5)  defects  in  appearance  of  the  fat-column. 

(1)  If  one  uses  test-bottles  not  provided  with  a  reg- 
ulator for  adjusting  the  level  of  the  fat-column,  the 
reading  of  the  percentage  of  fat  on  the  scale  may  be 
made  with  less  liability  of  error  by  measuring  the 
length  of  the  fat-column  with  a  pair  of  dividers,  one 
point  of  which  is  placed  at  the  bottom  and  the  other 
at  the  upper  limit  of  the  fat-column.     The  dividers 
are  then  removed  and  one  point  is  placed  on  the  zero 
mark  of  the  scale  on  the  bottle  used,  when  the  other 
point  will  be  at  the  exact  per  cent,  of  fat  in  the  milk 
tested. 

(2)  The  temperature  of  the  fat,  when  it  is  read  or 
measured,   should  be  above   120°   F.  and  not  above 
140°  R,  preferably  about  130°  F.     This  will  insure 
sharply  defined  upper  and  lower  limits  of  the  fat-col- 
umn.    In  case  the  contents  of  the  bottles  are  below 
120°  F.,  the  bottles  should  be  placed  for  15  or  20  min- 
utes in  water  that  has  a  temperature  of  130°  to  140°  F., 


THE    BABCOCK  TEST 


67 


before  the  reading  is  made.  This  usually  needs  to  be 
done  in  cold  weather,  when  hand-testers  are  used, 
especially  if  no  hot  water  has  been  placed  in  the  jacket 
during  the  whirling.  If  the  fat  is  above  150°  F.,  it 
should  be  allowed  to  cool  to  140°  F.  or  below  before 
reading  the  results.  Too  high  temperatures  give  too 
high  results,  because  the  fat-column  expands. 

(3)  The  line  of  division  between  the  fat-column  and 
the  liquid  beneath  is  nearly  a  straight  line  when  the 
testing  is  properly  done,  and  one  need  have  no  doubt 
about  the  reading  of  the  scale  at  this  point.  But  the 
upper  surface  of  the  fat-column  is 
concave  instead  of  straight,  which 
may  cause  some  uncertainty  as  to  the 
exact  point  at  which  the  reading 
should  be  made  on  the  scale.  The  J? 
correct  reading  is  taken  at  the  line 
where  the  upper  surface  of  the  fat- 
column  meets  the  sides  of  the  neck, 
the  very  highest  point  at  which  the 
fat-column  is  seen.  The  reading 
should  not  be  made  from  the  dark 
line  or  meniscus  lower  down,  which 
is  caused  by  the  refraction  of  the 
curved  surface.  The  points  at  which 
the  readings  should  be  made  are  shown 
in  Fig.  27,  indicated  as  A  and  B. 
Results  read  this  way  agree  with  those 
obtained  by  gravimetric  analysis.  The 
objection  may  be  raised  that  we  get  too  high  results 
by  reading  from  the  extreme  top  points  of  the  fat- 
column,  just  as  if  the  upper  surface  were  straight  at 


FIG.  27 

MEASURING 
FAT-COLUMN 


68  MODERN    METHODS   OF   TESTING   MILK 

these  points  instead  of  concave.  While  there  is  such 
an  apparent  error,  the  excessive  reading  thus  caused 
is  only  enough  to  make  up  for  the  loss  of  fat  which 
can  not  be  separated  from  the  rest  of  the  liquid  by 
centrifugal  force  and  brought  into  the  fat-column.  The 
amount  of  fat  thus  left  in  the  mixture  of  milk-serum 
and  acid  is  ordinarily  about  .2  per  cent,  and  this  is 
about  the  amount  of  excess  obtained  by  the  approved 
method  of  reading  the  upper  limit  of  the  fat-column. 

(4)  The  fat  appearing  in  the  neck  of  the  test-bot- 
tle at  the  end  of  a  successful  test  is  of  a  clear,  yellow 
color,  and  the  line  of  division  between  its  lower  limit 
and  the  acid  solution  beneath  it  is  sharply  distinct. 
However,  the  fat  is  apt  to  be  light-colored  in  the  case 
of  milk  from  cows  far  along  in  lactation. 

(5)  The  fat-column  may  show  certain  defects,  if 
the  conditions  of  the  test  have  not  been  properly  car- 
ried out,  among  which  are  (a)  black  particles  below 
or  above  or  in  the  fat-column,  or  a  darkened  appear- 
ance of  the  whole  column  of  fat;  (by  white  particles 
below  or  above  or  in  the  fat-column,  or  a  cloudy  ap- 
pearance of  the  whole  column;  and   (c)   bubbles  on 
the  surface. 

(a)  Black  particles  in  the  neck  of  the  test-bottle  at 
the  end  of  the  test,  or  a  darkened  appearance  of  the 
fat  itself,  are  due  to  one  or  more  of  the  following 
causes:  (i)  Too  strong  acid  (above  1.83  specific  grav- 
ity), (2)  too  much  acid  (more  than  18  cc.),  (3)  too 
high  temperature  of  the  milk  or  acid  (over  75°  F.), 
(4)  allowing  milk  and  acid  to  stand  in  test-bottle  too 
long  before  mixing,  (5)  allowing  the  acid  to  drop 


THE    BABCOCK    TEST  69 

through  the  milk  when  poured  into  the  test-bottle, 
(6)  interrupting  the  mixing  of  the  milk  and  acid  af- 
ter beginning  and  before  completion.  Black  particles 
can  usually  be  prevented  by  mixing  2  cc.  of  diluted 
glycerine  (80  cc.  of  glycerine  and  20  cc.  of  water) 
with  the  milk  before  adding  the  acid.  The  difficulty 
may  also  be  often  overcome  by  using  a  mixture  of 
equal  parts  of  water  and  sulphuric  acid  to  fill  the  bottle 
after  the  first  whirling. 

(b)  White  particles  of  undissolved  casein  below  or 
above  or  in  the  fat-column,  or  a  cloudy  appearance  of 
the  fat,  are  due  to  one  or  more  of  the  following  causes : 
(i)  Too  weak  acid  (below  1.82  specific  gravity),  (2) 
insufficient  amount  of  acid  (less  than  17  cc.),  (3)  too 
low  temperature  of  milk  or  acid  (below  60°  F.),  (4) 
incomplete  mixing  of  milk  and  acid,   (5)   insufficient 
speed  of  tester. 

Sometimes  when  the  fat  is  not  clear,  good  results 
may  be  obtained  by  allowing  the  bottles  to  cool  enough 
for  the  fat  to  harden  some,  and  then  warming  in  wa- 
ter at  140°  F.  before  reading. 

(c)  Bubbles  of  gas,  appearing  as  foam  on  the  top 
of  the  fat-column,  are  generally  due  to  the  use  in  the 
test-bottle  of  hard  water  containing  carbonates.     This 
condition  may  be  prevented  by  adding  to  the  water, 
previous  to  use,  a  few  drops  of  sulphuric  acid.    When 
the  foam  appears  and  interferes  with  the  reading,  a 
few  drops  of  alcohol  are  put  on  the  top  of  the  fat-col- 
umn and  the  reading  is  at  once  made.     The  alcohol 
.causes  the  bubbles  to  disappear  and  produces  a  sharp 
line  of  division  between  the  fat  and  alcohol.     If  the 
alcohol  is  allowed  to  be  in  contact  with  the  fat  for 


7O  MODERN    METHODS    OF    TESTING    MILK 

some  time  before  the  reading  is  made,  the  alcohol  and 
fat  mix  and  increase  the  height  of  the  fat-column,  thus 
producing  misleading  results. 

OUTLINE  STATEMENT  OF  SOME  SPECIAL 
PRECAUTIONS 

1.  Always  make  tests  in  duplicate. 

2.  Make  sure  that  the  sample  is  a  representative  one. 

3.  Have  the  temperature  of  the  milk  and  acid  at 
60°  to  70°  F.  before  putting  in  test-bottle. 

4.  Use  only  acid  of  right  strength. 

5.  Mix  milk  and  acid  thoroughly  as  soon  as  acid 
is  added. 

6.  Mix  a  second  time  after  a  short  interval. 

7.  Make  sure  that  the  tester  runs  at  right  speed 
and  does  not  jar. 

8.  Use  only  clean,  soft  water  in  filling  bottles. 

9.  Read  bottles  before  they  cool  and  at  about  130°  F. 

10.  To  insure  accuracy,  read  each  test  twice. 

SOME  MODIFICATIONS  OF  THE  BABCOCK  TEST 

One  frequently  sees  references  in  dairy  literature 
to  other  forms  of  tests  for  milk.  As  a  matter  of  in- 
formation, we  will  notice  a  few  of  the  modifications  of 
the  Babcock  test  together  with  other  forms  that  are 
in  use,  giving  good  results. 

The  Russian  Test. — This  is  a  modification  of  the 
Babcock  test,  differing  mainly  in  respect  to  some  of 
the  mechanical  details.  A  special  automatic  pipette  is 
used  (Fig.  28),  a  special  form  of  test-bottle  (Fig.  28a), 
the  neck  being  separate  from  the  rest  of  the  bottle,  and 


THE    BABCOCK    TEST 


also  a  special  form  of  acid-measure.  The  pipette  and 
acid-measure  are  one-half  the  usual  size.  The  milk  and 
acid  are  run  into  the  bottle  very  easily,  and  the  bot- 


FIG.  28 

AUTOMATIC  "RUSSIAN"  PIPETTE 


FIG.  28a 
"RUSSIAN"  TEST-BOTTLE 


ties  are  filled  with  hot  water  automatically  while  the 
machine  is  in  motion,  the  tester  also  being  of  a  special 
form. 

The  Gerber  Butyrometer, — Special  forms  of  tes- 
ter, test-bottle,  etc.,  are  used.  The  test  uses  1 1  cc.  of 
milk,  10  cc.  of  sulphuric  acid  (1.825  specific  gravity), 


72  MODERN    METHODS    OF    TESTING    MILK 

and  i  cc.  of  amyl  alcohol.  The  operations  are  carried 
out  about  the  same  as  in  the  Babcock  test. 

The  "Sinacid"  (no  acid)  Test.— The  distinctive  fea- 
ture of  this  test  is  that,  in  place  of  sulphuric  acid,  it 
uses  a  patented  mixture,  consisting  of  sodium  hydrox- 
ide (caustic  soda),  sodium  sulphate,  and  potassium 
sodium  tartrate  (Rochelle  salt)  which,  unlike  sul- 
phuric acid,  is  entirely  free  from  any  dangerous  pro- 
perties ;  it  uses  also  a  colored  alcoholic  solution.  After 
mixing  the  "sinacid"  liquid  with  the  milk,  the  mixture 
is  heated  to  200°  F.  for  5  minutes  before  being  whirled 
in  the  tester.  The  results  do  not  always  appear  to 
agree  closely  with  those  given  by  other  tests,  according 
to  the  reports  of  some  operators.  There  is,  moreover, 
some  natural  prejudice  against  using  a  process,  any 
part  of  which  is  patented. 

Gerber's  "Sal"  Test.— Gerber  has  described  a 
method  in  which  no  acid  is  used,  but  a  mixture  con- 
taining sodium  hydroxide,  common  salt  and  Rochelle 
salt ;  in  addition  a  small  amount  of  isobutyl  alcohol  is 
added. 

Wendler's  "New  Salt"  Method.— A  mixture  of 
neutral  salts  is  used  consisting  of  citrate  and  salicylate 
compounds. 


CHAPTER   V 

Method  of  Testing  Cream  by  the  Babcock  Test 

The  Babcock  test  can  be  used  in  ascertaining  the 
amount  of  fat  in  cream,  but  certain  modifications  and 
precautions  are  necessary  to  insure  correct  results  such 
as  (i)  special  form  of  test-bottle,  (2)  particular  care 
in  sampling  cream,  (3)  weighing  the  cream  to  be  used 
in  the  test  instead  of  measuring  it,  (4)  variations  in 
some  details  of  the  test  and  (5)  special  control  of  the 
meniscus. 

USE  OF  MILK-TEST  BOTTLES  IN  TESTING 
CREAM 

Milk-testing  bottles  can  be  used  in  testing  cream 
only  under  special  conditions.  Their  use  is  generally 
inconvenient  and  it  is  only  in  rare  cases  that  they  are 
ever  now  employed:  Cream  containing  over  8  or  10 
per  cent,  of  fat  will  fill  the  neck  of  the  test-bottle  too 
full  for  measurement,  when  we  take  18  grams  (about 
17.5  cc.)  to  test.  This  difficulty  may  be  overcome  in 
two  ways :  ( i )  By  using  a  sample  of  cream  less  than 
1 8  grams,  and  (2)  by  dividing  an  1 8-gram  sample 
into  roughly  equal  parts  between  two  or  more  bottles, 
according  to  its  richness  in  fat.  In  the  former  case 
the  per  cent,  of  fat  read  is  increased  by  a  correction 
to  be  considered  later  (p.  88).  In  the  second  case, 
the  tests  are  made  as  in  case  of  milk  and  the  per- 
centages found  in  the  different  bottles  are  added,  the 
sum  being  the  per  cent,  of  fat  in  the  cream  tested.  The 

73 


74  MODERN   METHODS  OF  TESTING   MILK 

volume  of  cream  in  each  test-bottle  is  always  made  up 
to  about  17.5  cc.  by  adding  water  to  the  cream  and 
mixing  before  adding  acid. 

SPECIAL    CREAM-TESTING    BOTTLES 

To  test  in  one  bottle  an  1 8-gram  sample  of  cream 
containing  over  10  per  cent,  of  fat,  the  neck  must  be 
made  to  hold  more  than  the  neck  of  a  milk-bottle,  that 
is,  more  than  2  cc.  This  additional  space  must  be  ob- 
tained (i)  by  using  a  neck  of  larger  diameter,  keeping 
the  length  the  same  as  in  the  milk-bottle  or  (2)  by 
making  the  neck  longer,  keeping  the  diameter  the  same, 
or  (3)  by  furnishing  the  neck  with  a  bulb  of  definite 
capacity. 

Different  kinds  of  bottles. — Cream  testing  bottles 
differ  mainly  in  the  construction  of  the  neck,  but  in 
some  cases  the  body  of  the  bottle  may  vary  in  shape 
and  size.  The  neck  varies  in  respect  to  shape,  length, 
capacity,  diameter  and  fineness  of  graduation.  The 
principal  varieties  of  cream-testing  bottles  on  the  mar- 
ket are  included  under  the  following  outlined  descrip- 
tion: (i)  The  neck  is  either  straight  throughout  its 
length  or  bulb-shaped  in  one  portion.  (2)  The  length 
of  bottle  varies,  being  usually  6  or  9  inches,  but  spe- 
.  cial  lengths  of  6^  'and  10  inches  are  made.  (3)  The 
graduated  scale  measures  20,  25,  30,  40,  50  and  55 
per  cent.,  usually  corresponding  to  a  capacity  varying 
from  4  to  ii  cc.  (4)  The  smallest  divisions  of  the 
scale  vary  from  0.2  to  I  per  cent.  (5)  The  gradua- 
tion is  directly  based  on  the  use  of  18  grams  of  cream 
in  some  cases  and  on  9  grams  in  others;  the  latter 
form  is  desirable  in  creamery  work. 


TESTING  CREAM   BY  THE  BABCOCK  TEST 


^"  9  GR.  50% 
CREAM -BOTTLE 


NECK  SHOWING 

GRADUATION   OF 

6^"    9    GR.    50% 

CREAM -BOTTLE 


9"  9  GR.   50% 

CREAM-BOTTLE 


FIG.    29 — STRAIGHT-NECKED    CREAM-BOTTLES 


MODERN    METHODS  OF  TESTING   MILK 


Requirements  for  bottles. — In  the  selection  of 
cream-testing  bottles,  certain  points  should  be  kept  in 
mind,  such  as  (i)  accuracy  of  reading,  (2)  ease  of 
reading,  (3)  convenience  of  handling  and  (4)  dura- 
bility. 

1 i )  Accuracy  of  reading. — The  accuracy  with  which 
the  percentage  of  fat  can  be  read  depends  upon  (a) 
the  diameter  of  the  neck,  (b)  the  length  of  the  neck 

and  (c)  the  amount  of  cream  used 
(9  or  1 8  grams).  The  larger  the  dia- 
meter of  the  neck,  other  conditions 
being  uniform,  the  greater  is  the  per- 
centage represented  by  each  division 
of  the  scale,  and,  consequently  the  less 
the  accuracy  of  reading.  The  longer 
the  neck,  other  conditions  being  the 
same,  the  smaller  is  the  percentage  of 
fat  represented  by  each  division  and, 
therefore,  the  greater  the  correctness 
of  the  reading.  The  length  and  dia- 
meter of  neck  being  the  same,  a  bottle 
with  neck  graduated  on  the  basis  of 
using  a  9-gram  sample  of  cream  per- 
mits more  accurate  reading  than  when 
based  on  18  grams.  For  accurate 
work,  no  bottle  should  be  used  in 
cream-testing  in  which  the  finest  divi- 
sion of  the  graduated  scale  represents 
more  than  0.5  per  cent. 

(2)  Ease  of  reading. — This  depends  mainly  upon 
the  diameter  of  the  neck;  the  greater  the  diameter, 
other  conditions  being  the  same,  the  more  difficult  is 


FIG.  290 

STRAIGHT-NECKED 

CREAM-BOTTLE 


TESTING  CREAM   BY  THE  BABCOCK  TEST 


77 


the  reading.  In  the  case  of  bulb- 
necked  bottles,  a  special  difficulty  is 
introduced  because  care  must  be  taken, 
when  water  is  added  near  the  close  of 
the  test,  so  that  neither  the  lower  nor 
upper  surface  of  the  fat-column  comes 
within  the  bulb,  making  it  obviously 
impossible  to  read  the  results  without 
further  manipulation. 

•(3)  Convenience  of  handling. — 
Bottles  with  shorter  necks  are  more 
convenient  to  handle;  they  are  rilled 
and  cleaned  more  easily  and  rapidly. 

(4)  Durability. — Shorter  bottles, 
when  properly  made,  are  more  dur- 
able. Long-necked  bottles  are  top- 
heavy  and  more  liable  to  be  overturned 
in  handling.  The  necks  of  bulb-necked 
bottles  are  more  easily  broken  than 
straight  necks. 

Owing  to  inconvenience  of  manipu- 
lation and  to  larger  breakage,  bulb- 
necked  bottles  are  little  used  now  in 
comparison  with  straight-necked  bot- 
tles. 

Best  forms  of  cream-testing  bot- 
tles.— Several  investigations  have 
shown  that  many  of  the  bottles  in  use 
at  creameries  are  wholly  incapable  of 
giving  sufficiently  accurate  results. 
The  latest  and  most  exhaustive  inves- 
tigation was  carried  out  by  Hunziker 


o 


n 
=1 

=./ 


/\ 


FIG.  30 
BULB-NECKED 
CREAM -BOTTLE 


78  MODERN   METHODS  OF  TESTING  MILK 

(Bull.  145,  1910,  Purdue  Agr.  Exp.  Sta.).  As  a  result 
of  this  work,  the  Official  Dairy  Instructors'  Association 
has  adopted  two  forms  of  standard  bottles  for  cream- 
testing,  (i)  50  per  cent.,  Q-gram,  so  called  6-inch 
bottle,  and  (2)  50  per  cent.,  g-gram,  so-called  Q-inch 
bottle,  a  detailed  description  of  which  is  given  on 
page  276. 

These  standard  cream-bottles,  have  several  advan- 
tages, .as  compared  with  the  ordinary  1 8-gram  bottles, 
among  which  are  the  following :  ( i )  Since  the  gradua- 
tion extends  to  50  per  cent.,  richer  cream  can  be  tested. 
(2)  There  is  greater  accuracy  in  reading  the  scale  of 
graduation,  since  it  is  possible  to  use  a  neck  of  smaller 
diameter,  thus  increasing  the  distance  between  the 
smallest  divisions  of  the  scale.  (3)  Decreased  dia- 
meter in  the  neck  makes  smaller  the  error  introduced 
by  the  meniscus,  when  this  is  not  eliminated  by  special 
treatment.  (4)  Direct  reading  of  the  percentage 
avoids  the  error  introduced  by  multiplying  the  read- 
ing by  2,  as  when  a  Q-gram  sample  is  tested  in  .an  18- 
gram  bottle.  (5)  The  body,  when  large  enough,  per- 
mits dilution  of  cream  with  water  before  adding  the 
full  amount  (17.5  cc.)  of  acid;  this  prevents  charring 
of  fat.  (6)  Some  cream  is  saved  when  the  tests  are 
promptly  made  with  each  delivery  in  place  of  compo- 
site tests,  the  annual  saving  being  appreciable. 

CREAM-TESTING  SCALES 

For  weighing  samples  of  cream,  a  set  of  accurate 
scales  is  required.  Different  forms  are  illustrated  in 
Figs.  31,  3 1  a,  32  and  32a.  Scales  with  agate  bearings 
are  much  preferable  to  other  forms,  since  the  agate 


TESTING  CREAM   BY   THE  BABCOCK   TEST 


79 


bearings  do  not  rust.  Bal- 
ances with  parts  liable  to  rust 
when  kept  in  damp  places 
become  in  time  unreliable 
for  accurate  work.  The 
scale  should  be  kept  in  per- 
fect condition  and  tested  for 
accuracy  from  time  to  time, 

by  comparing  with  some  balance  or  scales  of  known 
accuracy.  Scales  sensitive  to  one-tenth  and  one-twen- 
tieth of  a  gram  can  be  obtained. 


FIG.  31 
CREAM-TESTING  SCALES 


310 — CREAM-TESTING  SCALES 

THE  SAMPLING  OF  CREAM 

When  cream  to  be  tested  is  fresh  and  easily  made 
uniform  throughout,  its  mass  by  simple  mixing  or  pour- 
Mag,  it  is  not  difficult  to  secure  a  representative  sample. 
But,  with  the  introduction  of  the  method  of  separating 
cream  on  the  farm  and  delivery  to  shipping-stations 
or  through  cream-collectors,  conditions  are  often  intro- 
duced which  complicate  seriously  the  matter  of  obtain- 
ing representative  samples.  The  subject  will  be  dis- 
cussed under  the  following  divisions :  ( i )  Farm-sepa- 


8O  MODERN    METHODS  OF   TESTING   MILK 


FIG.   32 — CREAM -TESTING   SCALES 


rated   cream,    (2)    responsible   sampling   agents,    (3)' 
method  of  sampling,  (4)  amount  of  sample. 

Farm-separated   cream. — When  cream  is  directly 
delivered  fresh  at  the  creamery  the  sampling  is  easily 


FIG.   320 — TORSION   BALANCE   FOR   TWELVE   BOTTLES 


TESTING  CREAM   BY  THE  BABCOCK  TEST  8l 

managed.  When  the  cream  of  each  producer  is  first 
taken  to  .a  shipping-station  and  sampled  there  at  the 
time  of  delivery,  or  when  the  cream  is  collected  by  an 
agent  going  from  farm  to  farm  with  a  wagon  and  is 
sampled  at  the  farm,  difficulties  are  met.  The  trouble 
in  obtaining  samples  of  cream  under  these  conditions 
is  primarily  due  to  lack  of  care  of  cream  on  the  farm, 
which  results  in  souring,  thickening,  drying,  etc.,  con- 
ditions that  cause  lack  of  uniformity  in  consistency 
throughout  the  mass. 

Proper  conditions  for  producing  cream  that  can  be 
readily  sampled  may  be  outlined  as  follows:  Cream, 
separated  so  as  to  contain  about  40  per  cent,  of  fat,  is 
at  once  placed  in  cans  in  cold  water  and  kept  there,  in 
order  to  prevent  souring  in  warm  weather  and  freez- 
ing in  cold.  The  cream  is  stirred  occasionally  to  keep 
the  fat  well  distributed  and  to  prevent  drying  on  the 
surface.  It  should  be  delivered  at  the  creamery  at 
least  three  times  a  week  in  summer  and  twice  a  week 
in  cold  weather.  In  transporting  cream  that  is  to  be 
sampled  at  the  creamery  or  shipping-station,  the  cans 
should  be  full  enough  to  prevent  churning,  but  not  too 
full  to  prevent  thorough  mixing  of  the  cream  in  the 
can  previous  to  sampling. 

Responsible  sampling  agents. — It  has  been  found 
that  persons  charged  with  taking  samples,  such  as 
shipping-station  agents  and  cream  gatherers,  are  more 
often  than  not  lacking  in  ability  to  do  this  work  pro- 
perly, either  through  want  of  adequate  training  or 
through  insufficient  appreciation  of  the  importance  of 
details.  Thorough  instruction,  intelligence  and  care  in 
details  are  absolutely  requisite  in  this  work. 


82 


MODERN   METHODS  OF  TESTING  MILK 


Method  of  sampling. — When  cream  is  fresh  and  in 
condition  to  pour  easily,  it  is  prepared  for  sampling  by 
careful  and  complete  mixing,  which  is  accomplished  by 
pouring  cream  from  one  can  or  pail  to  another  or  by 
agitating  thoroughly  from  the  bottom 
up  with  an  efficient  stirrer  (Fig.  32b), 
or  by  a  combination  of  both  processes. 
The  sample  is  then  taken  with  the 
stirrer  or  with  a  cream-sampling  tube 
(Fig.  5  or  6,  p.  27),  which  must  be 
cleaned  for  each  sample  before  using ; 
cream  adhering  to  the  outside  of  the 
sampling-tube  is  allowed  to  drip  off 
before  transferring  the  contents  of  the 
tube  to  the  test  sample.  A  common 
way  is  to  stir  the  cream  thoroughly  in 
the  can  with  .a  stirrer,  then  pour  into 
the  weighing-can,  weigh  and  sample. 
When  cream  is  not  in  good  me- 
FIG  i2&  chanical  condition,  sampling-tubes 
COMBINED  CREAM  have  been  found  unsatisfactory.  In 
such  cases,  extra  care  is  taken  in  mix- 
ing the  cream  by  pouring  or  stirring, 
or  both,  and  taking  the  sample  with  the  stirrer. 

Frozen  cream  must  be  thawed  entirely  free  from 
ice  and  then  well  mixed  before  sampling.  Very  thick 
cream  should  be  warmed  until  it  pours  easily.  Par- 
tially churned  cream  can  not  be  sampled  with  satisfac- 
tory accuracy. 

Some  additional  details  will  be  found  helpful  in  the 
case  of  cream  collected  at  the  farm.  The  person  who 
collects  the  cream  is  equipped  with  (i)  a  spring- 


STIRRER    AND 
SAMPLER 


TESTING  CREAM  BY  THE  BABCOCK  TEST  83 

scale  for  weighing  cream,  (2)  a  weighing-pail  for 
weighing  each  farmer's  cream  separately,  (3)  a  com- 
bination stirrer  and  sampler  properly  constructed 
(Fig.  32b),  (4)  a  rubber  scraper. for  cleaning  cans, 
(5)  a -case  containing  sample-bottles  properly  num- 
bered and  arranged,  (6)  large  cans  into  which 
different  lots  of  cream  are  poured  after  weighing  and 
sampling,  (7)  a  record  book. 

At  each  dairy  the  collector  thoroughly  stirs  the  cream 
with  the  stirrer  and  then  pours  it  into  the  weighing- 
pail,  weighs  and  samples.  The  inside  of  the  weighing- 
pail  is  then  carefully  gone  over  with  the  rubber  scraper 
to  remove  as  far  as  possible  all  cream  adhering.  In 
case  the  patron  has  more  cream  than  can  be  weighed 
in  one  pail,  separate  weighings  are  made  and  a  sample 
is  taken  from  each  weighing,  the  different  samples 
being  placed  in  one  bottle.  The  sample  bottles  are  car- 
ried to  the  creamery  and,  if  possible,  the  testing  is 
done  the  same  day.  When  composite  samples  are  used, 
the  contents  of  each  sample-bottle  are  transferred  to 
the  corresponding  composite-sample  jar.  When  com- 
posite samples  of  cream  are  made  use  of,  aliquot  parts 
of  cream  should  be  taken  at  each  sampling  as  in  the 
case  of  milk  (p.  24)  ;  however,  a  sampling-tube  can 
not  be  used  for  this  purpose  unless  the  cream  is  in  first- 
rate  mechanical  condition.  The  best  device  for  taking 
aliquot  parts  of  cream  is  a  composite-test  gauge, 
which  consists  of  a  piece  of  brass  as  long  as 
a  sample  jar  and  which  is  graduated  on  both 
edges  into  divisions  indicating  the  amount  of 
cream  to  be  taken  from  the  lot  of  cream  sampled. 
This  gauge  is  attached  to  the  sample  jar  while  the 


84  MODERN   METHODS  OF  TESTING  MILK 

sample  is  being  taken  and  cream  is  added  to  the  jar 
until  it  rises  to  the  mark  representing  the  number  of 
pounds  of  cream  delivered. 

Amount  of  sample. — It  is  a  safe  precaution  to  take 
a  sample  sufficient  to  make  at  least  two  tests ;  from  i 
to  1^2  ounces  (30  to  45  cc.)  will  answer  the  purpose 
when  each  delivery  is  tested;  less  from  each  delivery 
will  answer  in  case  of  composite  sample. 

METHOD  OF  KEEPING  CREAM  SAMPLES 
In  general,  the  same  precautions  are  observed  in 
keeping  samples  of  cream  as  in  the  case  of  milk  (p. 
20),  whether  single  or  composite  samples.  Samples 
that  are  not  tested  soon  after  reaching  the  creamery 
should  be  treated  with  a  small  amount  of  preservative 
(p.  28).  With  thick  cream,  special  effort  should  be 
made  to  cause  the  preservative,  especially  bichromate, 
to  dissolve  completely  and  be  distributed  through  the 
sample.  This  may  be  done  by  agitating  the  cream 
carefully  by  a  gentle,  rotary  motion,  warming  slightly 
if  necessary.  With  composite  samples,  the  contents  of 
the  bottle  are  shaken  after  each  addition  of  cream  until 
there  is  a  complete,  uniform  mixture.  It  may  be  said, 
in  general,  that  lack  of  proper  care  of  cream  samples 
introduces  even  greater  errors  in  the  results  of  the  test 
than  is  the  case  with  samples  of  milk. 

AGE  OF  SAMPLES  WHEN  TESTED 
In  the  best-managed  creameries,  cream  is  delivered 
two  to  three  times  a  week  and  each  individual  ship- 
ment is  sampled  and  tested  on  the  day  of  delivery  or 
within  24  hours.  The  method  of  using  only  com- 
posite samples  in  cream-testing  is  gradually  being 


TESTING   CREAM   BY   THE   BABCOCK  TEST  85 

displaced ;  it  has  been  strongly  condemned  by  many  on 
the  basis  of  actual,  comparative  results.  While  it  pos- 
sesses the  single  advantage  of  reducing  the  cost  and 
work  of  testing,  the  disadvantages  connected  with  it 
entirely  overcome  this  one  advantage.  An  added  ad- 
vantage of  testing  each  delivery  of  cream  promptly, 
is  that  the  use  of  a  preservative  is  avoided  and  any 
unused  portion  of  the  cream  sample  left  can  be  poured 
back  into  the  cream-vat,  thus  avoiding  appreciable 
waste  when  large  numbers  of  samples  are  considered. 

PREPARATION  OF  SAMPLES  FOR  TEST 

If  the  cream  is  fresh  and  not  too  thick,  the  only 
preparation  required  to  make  the  sample  uniform, 
previous  to  weighing  sample,  is  to  give  the  bottle  a 
rotary  motion  "or  to  pour  the  cream  carefully. 

Very  thick,  heavy  cream,  often  found  in  case  of 
samples  kept  very  cold,  is  warmed  to  a  temperature  not 
above  85°  or  90°  F.,  then  poured  carefully  and  weighed 
quickly. 

As  recommended  by  Hills  (Bulletin  100,  Vermont 
Exp.  Sta.),  lumpy  cream  is  passed  through  a  small 
sieve  (Fig.  33),  such  as  is  commonly  used  in  kitchens. 
Any  remaining  lumps  found  in  the  sieve  are  rubbed 
through  the  meshes  by  the  fingers,  after  which  the 
cream  is  thoroughly  mixed  by  pouring  from  one  cup  to 
another.  The  sample  is  then  quickly  taken  for  testing. 

In  the  case  of  a  cream  sample  in  which  the  fat  is 
completely  separated,  or  churned,  or  is  changed  into 
a  tough,  leathery  consistency  (conditions  often  found 
in  carelessly-stored  composite  samples),  it  is  heated 
to  a  temperature  of  105°  to  110°  F.  to  melt  the  fat, 


86  MODERN    METHODS  OF   TESTING   MILK 

after  which  it  is  vigorously  and  continuously  shaken 
until  cooled  to  60°  F.  or  lower,  and  then  the  sample  is 
taken  and  weighed  as  quickly  as  possible.  Agitation 
during  the  process  of  cooling  is  essential  to  keep  the 
melted  fat  from  separating  so  rapidly  as  to  prevent 
obtaining  a  uniform  mixture. 

WHY  USE  OF  PIPETTE  IS  INACCURATE  FOR 
CREAM 

The  use  of  a  pipette  for  measuring  cream  samples 
is  inaccurate  for  the  following  reasons :  ( i )  More  fat 
adheres  to  the  inside  of  a  pipette  than  in  case  of 

milk,  the  er- 
ror     increas- 
ing with   the 
thickness   of   cream.      (2) 
The  weight  of  cream  de- 
creases as  the  per  cent,  of 
fat     in     cream     increases, 
FIG.  33  since    milk- fat    is    lighter 

CREAM-SAMPLING    SIEVE  ,,  ,,  ,,  ... 

than  the  other  constituents 

of  cream.  The  scale  of  the  test-bottle  is  based  on  the 
use  of  1 8  grams  of  material,  but  the  amount  of  cream 
that  occupies  the  volume  filled  by  18  grams  of  milk 
(17.5  cc.)  is  found  to  be  more  or  less  below  18  grams 
according  to  the  increased  percentage  of  fat  in  the 
cream,  running  even  below  17  grams  in  very  rich 
cream.  (3)  Separator  cream  is  more  or  less  filled  with 
bubbles  of  air,  and  ripened  cream  contains  gases  pro- 
duced by  fermentation.  These  decrease  the  weight  of 
a  given  volume  of  cream. 

For  the  preceding  reasons,  the  result  of  trying  to 


TESTING   CREAM    BY  THE   BABCOCK  TEST  87 

measure  by  pipette  a  sample  of  cream  to  be  used  for 
testing  its  fat  content  is  that  less  cream  will  be  used 
than  should  be,  and  therefore  the  results  will  be  too 
low.  Any  system  of  volumetric  measurement  pro- 
posed is  open  to  some  uncertainty  and  inaccuracy. 
The  use  of  a  pipette  in  testing  cream  is  justifiable  only 
for  work  that  is  not  expected  to  be  strictly  accurate. 

If  one  uses  a  pipette  in  measuring  cream  for  test- 
ing, accuracy  of  results  are  generally  improved  by 
measuring  18  cc.  of  cream  and  also  rinsing  the  pipette 
into  the  test-bottle  with  a  small  amount  of  water.  Pip- 
ettes are  obtained  which  have  an  18  cc.  mark  as  well 
as  a  17.6  cc. 

In  several  States,  laws  have  been  passed  making  it 
illegal  to  test  cream  in  any  other  way  than  by  weighing 
the  sample  to  be  tested,  when  the  fat  is  used  as  a  basis 
of  paying  for  cream. 

WEIGHING  SAMPLE  OF  CREAM 

Using  18  grams. — The  operation  of  weighing 
cream  is  simple.  One  places  the  empty  test-bottle  on 
one  pan  of  the  scales  and  balances  it  by  a  slide-weight 
or  some  form  of  counterpoise.  One  then  places  an 
i8-grarn  weight  on  the  other  pan,  after  which  the  pip- 
ette is  filled  with  cream  somewhat  above  the  17.6  cc. 
mark,  and  this  is  run  into  the  bottle,  the  last  portion 
being  run  in  more  slowly  until  the  two  scale-pans  just 
counterbalance  each  other.  A  little  practice  enables 
one  to  weigh  the  exact  amount  rapidly.  In  case  the 
amount  of  cream  taken  in  the  pipette  is  not  enough, 
agitate  the  sample,  draw  a  little  into  the  pipette  and 
run  this  slowly  into  the  bottle  until  it  counter-bal- 


88  MODERN   METHODS  OF  TESTING   MILK 

ances  the  weight.  In  case  too  much  cream  is  run 
into  the  bottle,  the  surplus  can  easily  be  withdrawn 
by  the  pipette.  No  cream  must  be  allowed  to  get  on 
the  outside  of  the  bottle  or  on  the  scale-pan  while  the 
weighing  is  done. 

Using  less  than  18  grams. — As  we  have  already  no- 
ticed, special  bottles  are  made  which  have  the  gradua- 
ted scale  based  upon  the  use  of  9-gram  samples,  and 
the  results  are  then  read  directly  from  the  neck  with- 
out any  kind  of  correction.  When,  however,  we  use 
9-grams  of  cream  in  a  bottle  made  for  an  i8-gram 
charge,  as  may  be  done  in  case  of  very  rich  cream, 
the  reading  of  the  fat-column  is  multiplied  by  2 ;  any 
error  in  the  test  is,  therefore,  doubled  in  the  final  re- 
sult. A  somewhat  inconvenient  method,  which  is  little 
used,  is  to  weigh  an  1 8-gram  sample  and  divide  it  be- 
tween two  cream  bottles,  in  which  case  water  is  added 
to  each  bottle  in  amounts  sufficient  to  bring  the  mixture 
to  about  18  cc.  in  volume.  The  results  of  the  test  in 
the  two  bottles  are  added. 

It  will  be  found  more  convenient  with  a  little  prac- 
tice to  weigh  exactly  9  or  18  grams  than  to  run  in  an 
approximate  amount  and  weigh  that  accurately. 

In  case  one  uses  in  1 8-gram  bottles  any  amount  less 
than  1 8  grams  for  a  sample,  it  is  necessary  to  correct 
as  follows  the  per  cent,  of  fat  read:  Divide  18  by  the 
number  of  grams  of  cream  used  and  multiply  the  result 
by  the  per  cent,  of  fat  read  in  the  test.  For  example, 
one  uses  13.5  grams  of  cream  and  the  result  reads  15.^ 
per  cent,  of  fat.  Divide  18  by  13.5  which  gives  1.33, 
and  multiply  this  by  15.6,  which  equals  20.8  per  cent., 
the  true  percentage  of  fat  in  the  sample. 


TESTING  CREAM   BY  THE  BABCOCK  TEST  89 

VARIATIONS  IN  DETAILS  OF  TEST 

In  carrying  out  the  details  of  the  Babcock  test  with 
cream,  some  of  the  details  require  modification  in  com- 
parison with  the  test  as  applied  to  milk.  The  points 
to  which  we  will  call  special  attention  in  this  connec- 
tion are  the  following:  (i)  Amount  of  acid  used,  (2) 
addition  of  water,  and  (3)  control  of  meniscus. 

Amount  of  acid. — The  amount  of  sulphuric  acid 
(p.  43)  that  is  needed  to  give  good  results  varies  some- 
what (i)  with  the  percentage  of  fat  in  the  cream,  or, 
stated  in  another  way,  with  the  percentage  of  solids 
not  fat,  and  (2)  with  the  temperature  of  cream  and 
acid.  In  illustration  of  the  first  point,  Hunziker  gives 
the  following  results  at  about  70°  F. : 

Per  cent  of  fat         Cream  Amount  of  acid  used, 

in  Cream.       Used  for  test.  Largest                    Smallest. 

50              18  grams  13     cc.                8     cc. 

50              9       "  7.5  cc.              4.5  cc. 

28             18       "  15     cc.             11     cc. 

28              9       "  8     cc.               5     cc. 

It  is  seen  that  for  any  one  sample  the  amount  of  acid 
used  can  be  varied  considerably  without  affecting  the 
results  of  the  test.  The  safest  guide  to  follow  in  de- 
ciding how  much  acid  to  use  is  the  color  of  the  cream 
and  acid  after  they  are  mixed.  The  mixture  of  cream 
and  acid  is  generally  lighter  in  color  at  first  than  in 
case  of  milk,  because  the  sugar  and  casein  are  less. 
Acid  can  be  added  until  the  mixture,  after  being  agi- 
tated, has  a  brownish  color,"  similar  to  that  produced  by 
mixing  coffee  and  cream.  It  is  usually  well  to  let  the 
bottle  stand  after  mixing  the  cream  and  acid  until  the 
mixture  turns  dark,  before  whirling.  Less  acid  can 


go  MODERN   METHODS  OF  TESTING   MILK 

be  used  at  higher  temperatures  and  more  at  lower 
(P.  43). 

It  is  the  custom  of  many,  when  using  less  than  18 
grams  of  cream,  to  add  enough  water  to  make  the 
volume  about  18  cc.,  mixing  well  before  adding  the 
acid.  This  calls  for  a  larger  amount  of  acid,  of  course, 
than  when  no  water  is  added  to  the  cream,  because  the 
water  weakens  the  acid. 

Addition  of  water  after  whirling. — A  cleaner  col- 
umn of  fat  is  usually  obtained  by  adding  water  twice 
after  the  first  whirling,  as  in  the  case  of  testing  milk 
(p.  64).  With  a  single  addition  of  water,  the  lower 
line  of  the  fat-column  is  cloudy-looking  and  uneven 
and  indistinct,  while  the  liquid  below  is  milky.  This 
condition  may  often  be  remedied  by  placing  the  bottles 
in  water  at  130°  to  140°  F.  for  15  or  20  minutes  be- 
fore a  final  whirling,  or,  if  this  fails,  the  fat  can  be 
solidified  by  placing  the  bottles  in  cold  water  after  the 
last  whirling  and  then  heated  to  130°  or  140°  F.  be- 
fore reading. 

Control  of  -meniscus  in  reading  fat-column, — There 
has  been  much  inaccuracy  introduced  into  the  testing 
of  cream  by  the  variable  factor  of  the  meniscus  in  the 
fat-column ;  the  details  of  the  trouble  need  not  be  dis- 
cussed here.  The  only  reliable  method  of  removing 
this  source  of  inaccuracy  is  to  get  rid  of  the  meniscus, 
changing  the  upper  curved  surface  of  the  fat-column 
into  a  flat  surface.  This  can  be  accomplished  by  the 
use  of  several  agents,  among  which  are  (i)  glymol, 
(2)  amyl  alcohol  and  (3)  alcohol  saturated  with  fat. 
When  any  one  of  these  solutions  is  placed  on  top  of  the 
fat-column,  it  keeps  separated  from  the  fat  but  re- 


TESTING  CREAM   BY  THE  BABCOCK  TEST  QI 

moves  the  meniscus,  leaving  a  straight  surface  as  a 
distinct  boundary  between  the  two  liquids.  This  makes 
it  easily  possible  to  read  the  top  of  the  fat-column  with 
a  satisfactory  degree  of  accuracy.  The  operation  of 
using  any  of  these  solutions  is  simple ;  a  small  amount 
is  dropped  into  the  opening  of  neck  of  the  bottle  so  as 
to  rest  upon  the  column  of  fat. 

(1)  Glymol  is  commonly  known   in  commerce  as 
white  mineral  oil,    (also  sold  under  other  names  as 
alboline,  blancoline,  glycoline,  etc.),  and  is  used  as  a 
lubricant    in    typewriters,    sewing-machines,    etc.      It 
costs  about  75  cents  a  gallon.     It  is  a  product  formed 
in  the  distillation  of  petroleum.    It  is  a  clear,  colorless, 
odorless  and  non-volatile  oil.     It  can  be  obtained  at 
any  drug-store.    The  glymol  can  be  added  to  the  test- 
bottle  just  before  the  results  are  read.     The  line  of 
division  between  glymol  and  the  top  of  the  fat-column 
can  be  made  sharper  by  coloring  the  glymol.     One 
ounce  of  crushed  alkanet  root   (obtainable  at  drug- 
stores)  is  wrapped  in  a  small  piece  of  cheese-cloth, 
placed  in  one  quart  of  glymol,  and  left  for  a  day  or 
two.    The  glymol  takes  on  a  bright  cherry  color.    Its 
use  has  been  thoroughly  investigated  by  Hunziker.    It 
may  be  added  that  Standard  Hand-Separator  Oil,  put 
up  by  the  Standard  Oil  Company,  gives  as  good  re- 
sults as  glymol. 

(2)  Amyl  alcohol,   colored   red  with   fuchsin,   has 
been  proposed  by  Eckles.    It  is  less  useful  than  glymol, 
since  amyl  alcohol  may  give  a  reading  somewhat  low 
on  account  of  dissolving  a  small  amount  of  fat. 

(3)  Alcohol  saturated  with  fat  has  been  used  at 
the  Wisconsin  Station.     It  is  made  by  shaking  a  tea- 


92  MODERN    METHODS  OF  TESTING   MILK 

spoonful  of  butter  with  about  6  ounces  of  denatured 
alcohol  or  of  wood  alcohol.  The  mixture  is  placed  in 
warm  water  and  slightly  warmed  and  then  shaken  until 
the  butter  ceases  to  dissolve.  This  solution  can  be 
slightly  colored,  if  desired. 


CHAPTER  VI 

Methods    of   Testing    Skim-Milk,     Buttermilk, 

Whey,  Ice-cream,  Condensed  Milk 

and    Powdered    Milk 

Dairy  products  such  as  ice-cream,  condensed  milk 
and  powdered  milk  can  be  tested  for  fat  by  the  Bab- 
cock  method,  and  also  by-products,  such  as  skim-milk, 
buttermilk  and  whey ;  but  in  general,  some  special  mo- 
difications are  necessary. 

METHOD  OF  TESTING  SKIM-MILK,  WHEY,  ETC. 

In  testing  materials  containing  only  .2  or  .3  per  cent, 
of  fat,  two  difficulties  are  experienced:  (i)  In  the 
ordinary  test-bottle,  the  reading  of  so  small  amounts 
of  fat  can  not  be  easily  done  with  accuracy.  (2)  Some 
fat  is  necessarily  left  in  the  mixture  of  acid  and  milk- 
serum,  which  may  constitute  an  important  factor  when 
the  total  fat  content  is  small. 

Special  forms  of  test-bottles  used  in  testing  whey, 
etc. — To  enable  one  to  make  readings  of  small  amounts 
of  fat  with  increased  accuracy,  special  forms  of  double- 
necked  test-bottles  have  been  devised,  which  are  so 
graduated  as  to  enable  readings  to  be  made  as  low 
as  .01  per  cent.  (Figs.  34  and  34a).  In  using  these 
bottles,  the  milk  and  acid  are  delivered  into  the  larger 
neck,  the  fat  being  driven  up  into  the  small  neck  by 
the  hot  water  added  toward  the  end  of  the  test. 

93 


94  MODERN   METHODS  OF  TESTING   MILK 

Enough  water  is  added  to  bring  the  fat-column  mto 
the  middle  of  the  small  neck.  In  mixing  milk  and 
acid  and  in  running  in  hot  water,  care  must  be  taken 
to  prevent  any  liquid  but  fat  going  into  the  small  neck 
or  fine  measuring-tube.  The  stoppers  in  the  bottles 


FIG.  34  FIG.  340 

BOTTLES   FOR  TESTING   SKIM-MILK 

are  used  to  adjust  the  fat-column  for  reading.  These 
double-necked  bottles  should  be  placed  in  the  tester 
in  such  .a  way  that  the  filling-tube  is  toward  the  center, 
thus  avoiding  the  danger  of  having  any  fat  caught 
between  this  tube  and  the  side  of  the  bottle  when  re- 
suming the  upright  position  after  whirling. 

Separating  fat  from  mixture  in  bottle. — Attention 
has  previously  (p.  68)  been  called  to  the  difficulty  ex- 
perienced in  separating  all  the  fat  from  the  mixture 


TESTING  SKIM   MILK,  BUTTERMILK,  ETC.  95 

of  acid  and  milk-serum.  Under  ordinary  conditions 
of  working,  materials  low  in  fat,  like  skim-milk,  may 
fail  to  give  up  to  the  fat-column  .05  or  even  .1  per 
cent,  of  fat.  Some  double  the  reading  of  fat  when  it 
is  below  .1  per  cent,  in  order  to  make  allowance  for 
the  unseparated  fat.  The  fat  may  be  separated  from 
the  rest  of  the  liquid  more  completely  by  proceeding 
as  follows :  Use  20  cc.  of  sulphuric  acid,  whirl  the  bot- 
tles at  full  speed  3  to  5  minutes  longer  than  usual  and 
read  the  fat  when  at  a  temperature  of  130°  to  140°  F. 
Steam-turbine  testers,  which  keep  the  bottles  hot,  give 
best  results.  Any  test  of  these  by-products  showing 
less  than  .05  per  cent,  of  fat  is  open  to  the  suspicion 
of  being  defective. 

Skim-milk  and  buttermilk  are  treated  alike.  In 
working  with  whey,  it  is  noticeable  that  after  adding 
acid  the  mixture  turns  dark  very  slowly,  due  to  the 
presence  of  less  sugar  and  to  the  absence  of  casein. 
Less  than  the  usual  amount  of  acid  is  sufficient  for 
whey,  8  or  10  cc.  frequently  being  sufficient. 

METHOD  OF  TESTING  ICE-CREAM 

In  applying  the  Babcock  test  to  the  determination 
of  fat  in  ice-cream,  the  regular  method  of  procedure 
must  be  modified  in  such  a  way  as  to  prevent  undue 
charring  of  the  sugar.  Of  the  methods  in  use,  we  will 
describe  three,  one  by  White  (Pennsylvania  State 
College),  one  by  Holm  (Chicago  Dep't  of  Health), 
and  the  other  by  Ross  (Cornell  Univ.  Coll.  of  Agr.). 

Whatever  method  is  used,  trie  same  process  of  tak- 
ing and  preparing  samples  applies  to  all.  A  special 
sampling-tube  or  a  butter-trier  can  be  used  in  drawing 


96  MODERN    METHODS  OF   TESTING   MILK 

samples,  several  plugs  being  drawn  and  placed  in  the 
sample  jar.  The  jar  containing  the  material  is  then 
placed  in  water  heated  to  80°  F.  and  agitated  with  a 
rotary  motion  until  the  ice-cream  is  melted.  The  mel- 
ted cream  is  then  poured  through  a  cream-sampling 
sieve  (Fig.  33,  p.  86)  into  a  cup  or  beaker,  any 
lumps  being  rubbed  through  with  the  fingers.  The 
sample  is  then  thoroughly  mixed  by  pouring  several 
times  from  one  beaker  to  another  and  the  weighing  is 
made  at  once  as  in  the  case  of  cream  (p.  87). 

The  method  of  testing  described  by  White  is  essen- 
tially as  follows :  A  6-gram  sample  is  weighed  into  an 
ordinary  milk-testing  bottle.  With  a  6-gram  sample, 
one  adds  4  cc.  of  sulphuric  acid  (sp.  gr.  1.83)  and 
carefully  mixes  the  cream  and  acid;  after  about  two 
minutes,  one  adds  4  cc.  more  of  acid  and  again  care- 
fully mixes.  The  mixture  should  be  of  a  light-brown 
color;  if  it  should  be  black,  the  test  should  be  begun 
again,  another  sample  being  weighed  and  less  acid 
used.  The  bottle  is  at  once  placed  in  the  steam  cen- 
trifuge and  whirled  as  rapidly  as  possible  for  three 
minutes.  The  test  is  then  completed  by  addition  of  hot 
water  and  repeated  whirling.  It  is  best  to  add  the  hot 
water  in  two  portions,  whirling  three  minutes  after 
the  first  .addition  of  water  and  two  minutes  after  the 
second  addition.  The  percentage  of  fat  shown  is  mul- 
tiplied by  three. 

In  Holm's  method,  a  mixture  of  equal  parts  of  hy- 
drochloric and  80  per  cent,  acetic  acid  is  substituted  for 
sulphuric  acid.  A  sample  of  9  grams  is  weighed  into  a 
milk-testing  bottle,  and  30  cc.  of  the  acid  mixture 
added.  The  bottle  is  then  placed  in  hot  water  and 


TESTING  SKIM  MILK,  BUTTERMILK,  ETC.  97 

kept  there  until  the  contents  are  well  darkened  but  not 
charred.  The  test  is  completed  in  the  usual  manner. 
The  fat-reading  is  multiplied  by  2. 

The  method  of  Ross  is  as  follows :  Mix  thoroughly 
equal  weights  of  melted  ice-cream  and  water  at  100° 
F.  Weigh  9  grams  of  the  diluted  cream  (containing 
4.5  grams  of  ice-cream)  into  a  cream-testing  bottle, 
preferably  a  9-gram  bottle  with  a  body  of  the  same  size 
as  that  of  an  i8-gram  bottle,  though  a  regular  i8-gram 
bottle  can  be  used.  To  the  contents  of  the  bottle  add 
17.5  cc.  of  glacial  acetic  acid  and  agitate  2  or  3  minutes. 
Then  .add  15  cc.  of  sulphuric  acid  (sp.  gr.  1.82-1.83) 
and  agitate  about  a  minute.  Complete  the  test  in  the 
usual  way.  Since  the  amount  of  ice-cream  used  is 
4.5  grams,  the  result  is  multiplied  by  2  if  a  9-gram 
bottle  is  used  and  by  4  for  an  1 8-gram  bottle. 

METHOD    OF    TESTING    UNSWEETENED    CON- 
DENSED   MILK 

The  most  effective  adaptation  of  the  Babcock  method 
to  the  determination  of  fat  in  unsweetened  condensed 
milk  is  that  worked  out  by  Hunziker  (Bull.  134,  Ind. 
Exp.  Sta.).  Dilute  the  sample  of  milk  with  an  equal 
weight  of  water  and  weigh  9  grams  of  this  diluted 
milk  into  a  Babcock  milk-testing  bottle  (graduated  to 
10  per  cent.)  and  add  one-half  of  a  pipetteful  of  water 
(about  9  cc.).  Then  add  17.5  cc.  of  sulphuric  acid 
and  agitate  until  the  curd  dissolves  completely  and 
whirl,  as  in  testing  milk,  for  5  minutes.  Then  fill  bottle 
to  the  zero  mark  with  hot  dilute  sulphuric  acid, 
made  by  mixing  equal  parts  of  sulphuric  acid  and  wa- 
ter, adding  the  acid  to  the  water  (p.  44).  (Where 


98  MODERN   METHODS  OF  TESTING   MILK 

only  one  or  two  tests  are  made,  one  pipetteful  of  water 
and  one  acid  measure  full  of  acid  answer  the  purpose.) 
The  bottles  are  then  whirled  for  2  minutes,  filled  with 
hot  water  to  about  the  8  per  cent,  mark,  and  whirled 
again  for  i  minute;  the  reading  is  made  at  140°  F. 
from  the  bottom  of  the  lower  meniscus  to  the  extreme 
top  of  the  upper  meniscus.  The  result  is  multiplied 
by  4. 

For  accurate  results,  weighing  the  sample  is  indis- 
pensable. Approximate  results  can  be  obtained  by 
diluting  a  measured  .amount  of  condensed  milk  with 
three  volumes  of  water  and  agitating  until  the  mixture 
is  uniform.  A  17.6  cc.  sample  of  this  is  taken  and  the 
process  above  described  followed. 

For  condensed  milk  containing  added  sugar, — 
Many  brands  of  condensed  milk  contain  added  cane 
sugar,  which  in  testing  is  so  blackened  by  the  acid  as 
to  make  the  results  unreliable.  This  trouble  can  be 
overcome  by  special  treatment  devised  by  Farrington. 
Dissolve  40  grams  of  condensed  milk  in  enough 
water  to  make  100  cc.  of  solution.  With  a  17.6  cc. 
pipette,  measure  the  same  amount  as  for  a  milk 
test  into  a  milk-testing  bottle.  Add  about  3  cc. 
of  the  sulphuric  acid  used  in  the  test  and  mix  the  acid 
and  milk  by  shaking  vigorously.  The  acid  is  added 
to  coagulate  the  curd  and  enclose  the  fat,  allowing 
the  sugar  to  separate  in  the  surrounding  liquid.  The 
curd  is  compacted  into  a  lump  by  whirling  the  test- 
bottles  in  a  steam-turbine  tester  at  high  speed  and  at 
a  temperature  of  200°  F.  After  this  whirling,  the 
bottles  are  taken  from  the  tester  and  the  liquid  portion, 
containing  much  of  the  sugar,  is  carefully  poured 


TESTING  SKIM  MILK,  BUTTERMILK,  ETC.  99 

from  the  neck  without  breaking  the  lump  of  curd. 
Then  an  addition  of  10  cc.  of  water  is  made  to  the 
test-bottles,  the  curd  is  shaken  up  to  wash  out  more 
sugar,  and  again  3  cc.  of  sulphuric  acid  added.  The 
bottles  are  again  whirled  and  the  liquid  portion  de- 
canted. Then  the  test  is  completed  by  adding  10  cc. 
of  water,  17.5  cc.  of  sulphuric  acid,  and  proceeding  as 
usual.  Correct  the  fat-reading  by  multiplying  by  18 
and  dividing  by  7. 

METHOD  OF  TESTING  DRIED  MILK,  MILK 
POWDER,  ETC. 

Successful  means  of  drying  milk  have  recently  been 
devised,  and  products  are  appearing  on  the  market  in 
the  form  of  dried  skim-milk  and  whole  milk.  These 
materials  are  in  the  form  of  fine  flaky  or  powdery 
substances.  Owing  to  the  great  advantages  of  hand- 
ling milk  in  such  forms,  these  products  are  destined 
to  find  extensive  use,  and  the  desirability  of  testing 
them  is  obvious. 

The  Babcock  test,  when  applied  to  these  materials, 
gives  results  much  below  the  truth.  Various  attempts 
have  been  made  to  adopt  the  Babcock  test  to  these 
products,  the  most  satisfactory  of  which  is  that  of 
Redmond  (Journal  of  Industrial  and  Engineering 
Chemistry,  Vol.  4  (1907),  page  544).  Weigh  2.5 
grams  of  milk  powder  and  transfer  it  to  an  ordinary 
10  per  cent.  Babcock  milk-bottle.  A  small  glass  funnel 
is  useful  in  transferring  the  powder.  Add  31  cc.  of 
dilute  sulphuric  acid  (made  by  pouring  395  cc.  of  con- 
centrated acid  into  605  cc.  of  water)  and  place  the 
bottle  upright  in  a  dish  of  gently  boiling  water.  Shake 


IOO  MODERN    METHODS  OF   TESTING    MILK 

frequently  and  keep  in  the  boiling  water  until  all  the 
powder  is  dissolved  and  the  solution  is  dark  brown  in 
color,  which  usually  requires  7  to  10  minutes.  After 
removing  the  bottle  from  the  water  add  12  cc.  of  strong 
sulphuric  acid  (sp.  gr.  1.82  to  1.83)  and  mix  thorough- 
ly, by  agitation  with  a  rotary  motion  taking  care  to  keep 
the  solution  from  getting  into  the  neck  of  the  bottle. 
Place  the  bottle  in  a  centrifuge  and  whirl  4  or  5  min- 
utes. Add  hot  water  until  the  solution  reaches  the 
lower  end  of  the  neck,  whirl  again  for  I  minute  and 
then  add  hot  water  until  the  fat  rises.  Finally  whirl 
again  i  minute.  Read  fat  column  at  130°  to  140°  F. 
Readings  should  be  made  to  0.05  per  cent,  on  the  grad- 
uated scale.  The  reading  is  multiplied  by  7.2  to  ob- 
tain the  percentage  of  fat  in  the  material  tested. 


CHAPTER  VII 

Methods  of  Testing  Butter  and  Cheese  for  Fat 

The  Babcock  test  has  not  been  adapted  to  determine 
the  amount  of  fat  in  butter  as  accurately  as  in  case  of 
other  milk  products.  A  mass  of  butter  is  so  variable 
in  composition,  owing  to  the  uneven  distribution  of 
water,  that  it  is  difficult  to  obtain  a  representative 
sample  when  only  a  small  amount  is  used.  Other 
specific  conditions  which  make  the  application  of  the 
Babcock  method  less  satisfactory  than  in  case  of  other 
dairy  products  we  need  not  consider  in  detail.  Ap- 
proximate results  can  be  obtained  by  observing  cer- 
tain precautions. 

PREPARATION  OF  SAMPLE  OF  BUTTER 

Whatever  constituent  of  butter  is  determined  and 
whatever  method  is  used,  extreme  care  must  be  exer- 
cised in  taking  and  preparing  samples  for  testing. 

With  a  butter-trier  draw  from  different  parts  of  the 
package  or  mass  several  portions  of  butter  aggregating 
4  to  8  ounces.  Place  these  portions  in  a  fruit-jar  or 
composite-sample  bottle,  melt  completely  by  placing 
the  closed  jar  in  water  at  100°  to  110°  F. ;  then  remove 
from  the  warm  water  and  shake  vigorously  for  one  or 
two  minutes,  after  which  moderate  agitation  is  con- 
tinued until  the  butter  solidifies.  The  cooling  may  be 
hastened  by  holding  the  jar  under  a  stream  of  cold 

101 


IO2  MODERN   METHODS  OF  TESTING   MILK 

water,  continuing  to  shake  the  bottle  vigorously  until 
the  butter  hardens. 

Another  method  is  to  place  the  jar  containing  the 
butter  in  water  at  100°  to  110°  F.,  leaving  it  only  until 
the  butter  just  begins  to  melt.  With  a  long  knife  or 
spoon  mix  the  melted  and  unmelted  portions  as  com- 
pletely as  possible.  Then  replace  the  jar  in  the  warm 
water  until  melting  begins  again,  remove  from  the 
water  and  stir  thoroughly  as  before.  The  process  of 
softening  and  mixing  is  repeated  until  the  sample  con- 
tains no  lumps  and  the  consistency  of  the  mass  is  about 
like  that  of  thick  cream.  The  jar  is  then  placed  in 
cold  water  and  the  sample  vigorously  stirred  while  the 
butter  is  hardening.  Care  must  be  taken  to  keep  the 
butter  scraped  off  the  sides  of  the  jar  where  it  begins 
to  harden  more  quickly  than  toward  the  center.  When 
the  sample  has  cooled  to  a  consistency  about  like  that 
of  ordinary  butter,  the  stirring  is  discontinued.  The 
jar  is  then  kept  closed  except  when  removing  a  sample 
for  weighing. 

MODIFIED  BABCOCK  TEST  FOR  BUTTER 

For  strictly  accurate  results  gravimetric  methods 
must  be  used.  Where  only  approximate  correctness 
is  desired,  some  modification  of  .the  Babcock  test  will 
answer. 

On  a  cream-scale  place  a  bottle  of  the  kind  shown 
in  Fig.  35  or  one  of  similar  construction.  After  bal- 
ancing the  bottle,  take  small  pieces  of  butter  on  the 
point  of  a  knife  from  different  parts  of  the  sample  in 
the  jar,  prepared  as  described  in  the  previous  section, 
and  place  them  in  the  funnel-shaped  tube  of  the  bottle 


TESTING  BUTTER  AND  CHEESE  FOR  FAT 


103 


until  the  test  sample  weighs  9  grams.  The  bottle  is 
then  placed  in  hot  water  until  the  butter  melts  and  runs 
into  the  body  of  the  test-bottle.  The  fat  adhering  to 
the  inside  walls  of  the  funnel  is  washed  down  into  the 
bottle  with  8.8  cc.  (one-half  pipetteful)  of  hot  water, 
and  the  same  amount  (8.8  cc.)  of  sul- 
phuric acid  is  added.  After  the  contents 
are  thoroughly  mixed,  the  bottle  is 
placed  in  a  centrifuge  and  whirled  for 
about  5  minutes.  To  read  the  result, 
the  funnel-shaped  tube  is  rilled  with  hot 
water,  which  raises  the  fat-column  into 
the  graduated  neck.  By  gently  pressing 
down  or  gently  drawing  up  the  rubber 
cork  at  the  top  of  the  graduated  neck, 
the  fat-column  may  be  moved  down  or 
up  in  the  graduated  neck  so  as  to  bring 
the  lower  end  of  the  column  level  with 
the  zero  mark,  which  is  indicated  by  a 
ring  below  the  bulb.  The  percentage  of 
fat  is  read  directly.  Before  making  the 
final  reading,  let  the  bottle  stand  for  10 
minutes  in  water  at  120°  F.  With  care- 


FIG.  35 
BOTTLE  FOR  USE 

IN    TESTING 

BUTTER        ful    attention  to   all   details,    results   of 
approximate  accuracy  can  be  obtained. 


SHAW  TEST  FOR  FAT  IN  BUTTER 

This  method  was  devised  by  R.  H.  Shaw,  chemist 
in  the  Dairy  Division  of  the  Bureau  of  Animal  Indus- 
try, U.  S.  Department  of  Agriculture  (Circular  202). 
It  is  a  strictly  gravimetric  method,  not  only  the  sam- 
ple of  butter  being  weighed  but  also  the  amount  of 


104  MODERN   METHODS  OF  TESTING   MILK 


FIG.  36— DOUBLE  SOCKET  WITH  FUNNELS  IN  POSITION 
B,  view  of  socket  from  below.  Care  must  be  taken  that  the  capillary 
stem  of  the  funnel  does  not  project  far  enough  through  the  hole  at  the 
bottom  of  the  socket  to  strike  against  the  side  of  the  centrifuge  when 
whirling.  A  rubber  gasketing  should  be  fitted  to  the  bottom  of  the 
socket. 


TESTING  BUTTER  AND  CHEESE  FOR  FAT 


105 


purified  fat  that  is  obtained.  In  brief  outline  the 
method  is  as  follows :  The  salt  and  part  of  the  curd 
are  first  removed  from  the  butter  with  hot  water; 
the  remaining  curd  is  dissolved  in  dilute  sulphuric 
acid,  the  acid  solution  is  removed  from  the  fat  and  the 
latter  weighed. 

Apparatus  required :  ( i )  Babcock  centrifuge  with 
special  sockets  providing  openings 
in  side  (Fig.  36).  (2)  A  special 
separatory  funnel  (Fig.  36a). 
(3)  A  balance  sensitive  to  o.oi 
gram  (a  torsion  balance  in  good 
condition,  such  as  is  used  in  mois- 
ture tests,  will  answer).  (4)  An 
accurate  set  of  metric  weights. 
(5)  A  10  cc.  graduated  glass  cy- 
linder. (6)  A  100  cc.  glass  beaker. 
Operation  of  test. — The  opera- 
tions required  to  perform  the 
details  of  the  test  are  as  follows : 
(i)  Weighing  sample,  (2)  trans- 
\  /  A  ferr*n£  weighed  sample  to  separa- 
te -f^A/C^.  / 1  tory  funnel,  (3)  whirling,  (4) 
removal  of  water,  (5)  dissolving 
of  curd,  (6)  separation  of  fat 
from  acid  solution,  (7)  determina- 
tion of  percentage  of  fat,  (8) 
cleaning  funnels. 

SEPARATORY  FUNNEL  *        .        . 

WITH  CAPILLARY  STEM     (i)  Weighing  sample. — Count- 
erpoise the  small  beaker  on  the 
balance  and  carefully  weigh  20  grams  from  the  sample 
prepared  as  already  described  (p.  101). 


IO6  MODERN   METHODS  OF  TESTING   MILK 

(2)  Transferring  weighed  sample  to  funnel. — Pre- 
vious to  use,  each  separatory  funnel,  clean  and  dry, 
must  be  weighed  accurately  and  a  record  kept  of  the 
weight  of  each.    In  order  to  transfer  the  butter  from 
the  beaker  to  the  funnel,  the  butter  in  the  beaker  is 
melted   by   warming  either  by   addition  of   a   small 
amount  of  boiling  water  or  by  putting  in  a  warm  place. 
The  melted  sample  should  then  be  poured  without  loss 
into  the  funnel,  which  must  be  held  upright.     The 
sides  of  the  beaker  are  rinsed  with  a  fine  stream  of  hot 
water,  using  not  more  than  a  teaspoonful  each  time, 
and  the  rinsings  poured  into  the  funnel;  this  treat- 
ment is  repeated  until  the  funnel  is  full  to  within  one- 
quarter  of  an  inch  of  the  shoulder. 

(3)  Whirling. — The  separatory  funnel  is  then  in- 
serted in  the  special  socket  of  the  centrifugal,  allowing 
the  stem  to  project  through  the  hole  in  the  bottom, 
and  the  handle  of  the  stop-cock  through  the  open  side, 
(the  socket  always  being  placed  in  the  centrifuge  with 
the  open  side  facing  in  the  direction  in  which  the  wheel 
revolves,    in   order   to   prevent   the    stop-cock  being 
thrown  out  and  broken).    The  funnel  is  whirled  one 
minute  at  the  speed  used  in  testing  milk  (p.  41).    The 
centrifuge  must  be  kept  warm. 

(4)  Removal  of  water. — The  funnel  is  taken  from 
the    centrifuge   and    the    water    is    allowed    to   flow 
through  the  stop-cock.    Most  of  the  salt  and  some  of 
the  curd  are  taken  out  by  the  water.    The  rest  of  the 
curd  and  all  of  the  fat  remain  in  the  funnel.     (Care 
must  be  taken  to  keep  the  stop-cock  always  under  con- 
trol, so  that  it  can  be  closed  at  the  right  instant  and 
thus  prevent  fat  running  out  and  consequent  loss  of 


TESTING  BUTTER  AND  CHEESE  FOR  FAT 


the  test.  Control  of  the  stop-cock  can  be  maintained 
by  giving  it  frequent  and  slight  movements  while  the 
water  or  acid  is  running  through  it.) 

(5)  Dissolving  the  curd.  —  Into  the  beaker  pour  9 
cc.  of  cold  water;   then  add  n  cc.  of  sulphuric  acid 
(sp.  gr.  1.82  to  1.83)  and  mix  by  gentle  shaking.   This 
mixture  is  added  at  once,  before  cooling,  to  the  con- 
tents of  the  funnel  and  then  this  is  given  a  rotary 
motion,  with  the  hand  grasping  the  neck,  until  the  curd 
is  completely  dissolved.    It  is  then  whirled  in  the  cen- 
trifuge one  minute,  after  which  the  acid  solution  is 
drawn  off  until  the  layer  of  fat  is  within  a  quarter  of 
an  inch  of  the  stop-cock.     The  operation  of  treating 
with  a  mixture  of  acid  and  water,  whirling,  etc.,  is 
repeated. 

(6)  Separation  of  fat.  —  The  fat  now  appears  as  a 
clear,  transparent  layer,  free  from  curd,  and  the  solu- 
tion below  it  is  practically  colorless.    To  separate  these 
two,  draw  off  the  latter  until  the  fat  nearly  reaches 
the  stop-cock,  and  whirl  again  for  one  minute.    Then 
draw  off  the  solution  again  until  the  fat  just  reaches 
the  end  of  the  capillary  stem,  care  being  taken   to 
keep  the  working  of  the  stop-cock  under  complete  con- 
trol. 

(7)  Determination  of  percentage  of  fat.  —  The  out- 
side of  the  separatory  funnel  is  completely  dried  by 
wiping  with  a  dry  cloth  and  the  funnel  is  then  weighed. 
The  weight  of  the  funnel  and  fat,  minus  the  weight  of 
the  empty  funnel,  gives  the  weight  of  fat  in  the  20- 
gram  sample.     This  result,  multiplied  by  5  gives  the 
percentage  of  fat  in  the  butter  tested. 

(8)  Cleaning  funnels.  —  After  completing  each  test, 


IO8  MODERN   METHODS  OF  TESTING   MILK 

the  separatory  funnels  should  be  thoroughly  cleaned. 
This  is  easily  done  with  hot  water  together  with  soap 
or  cleaning-powder,  after  which  the  funnels  are  well 
rinsed  with  clean  water  and  allowed  to  drain. 


PREPARATION  OF  SAMPLE  OF  CHEESE 

Since  different  portions  of  the  same  cheese  vary  in 
composition,  special  means  must  be  used  to  get  a 
representative  sample.  The  sample  for  testing  is  pre- 
pared as  follows:  When  a  cheese  can  be  cut,  a  nar- 
row, wedge-shaped  segment  is  taken,  reaching  from 
the  outer  edge  to  the  center.  This  is  cut  into  strips 
and  passed  through  a  meat-grinding  machine  two  or 
three  times.  This  mass  is  carefully  mixed,  and  from 
this  a  sample  is  weighed. 

When  cheese  can  not  be  cut,  samples  are  obtained 
by  a  cheese-trier.  If  possible,  three  plugs  should  be 
drawn,  one  at  the  center,  one  about  an  inch  from  the 
outer  edge,  and  one  at  a  point  half  way  between  the 
two.  If  only  one  plug  can  be  drawn,  this  should 
be  taken  at  a  point  about  half  way  between  the  mar- 
gin and  center.  The  plugs  should  be  taken  perpen- 
dicular to  the  end  surface  of  the  cheese  and  should 
reach  either  entirely  through  the  cheese  or  just  half 
way.  The  plugs  should  be  made  fine  by  grinding  or 
cutting  and  carefully  mixed  before  weighing  samples. 
In  preparing  samples,  they  should  not  be  exposed  to 
the  air  longer  than  necessary,  since  loss  of  moisture 
should  be  prevented  as  much  as  possible  before  weigh- 
ing. 


TESTING  BUTTER  AND  CHEESE  FOR  FAT  ICX) 

BABCOCK  TEST  FOR  CHEESE 

From  the  sample  prepared  in  the  manner  described 
in  the  preceding  section,  weigh  a  Q-gram  sample  into 
a  cream-testing  bottle  or  a  4.5-gram  sample  into  an 
ordinary  milk-testing  bottle. 

In  the  case  of  well-ripened,  softened  cheeses  of  the 
hard  varieties  and  in  the  case  of  all  soft  varieties,  the 
following  method  is  appplicable:  Add  about  15  cc.  of 
hot  water  to  the  test-bottle  and  agitate  until  the  cheese 
is  disintegrated ;  this  can  be  hastened  by  adding  a  few 
cubic  centimeters  of  sulphuric  acid  and  keeping  the 
bottle  in  warm  water.  When  no  more  lumps  are  seen 
in  the  mixture,  add  17.5  cc.  of  sulphuric  acid.  The 
test  is  then  completed  in  the  usual  way,  making  cor- 
rection in  reading  when  necessary  (p.  88). 

In  cheese-curd  and  unripened  hard  cheese,  the  fore- 
going method  requires  too  much  time  to  dissolve  the 
curd,  and  for  such  cases  Sammis  finds  the  following 
method  to  work  rapidly  and  satisfactorily:  To  the 
weighed  Q-gram  sample  of  cheese  in  a  cream-testing 
bottle  add  10  cc.  of  water  at  125°  to  135°  F.  and  then 
at  once  add  sulphuric  acid  at  first  in  small  portions  of 
about  i  cc.  each,  agitating  vigorously  after  each  addi- 
tion. The  addition  of  acid  is  continued  until  17.6  cc. 
has  been  used.  Loss  by  spurting  is  avoided  by  adding 
the  acid  in  small  portions  at  first.  By  the  time  all  the 
acid  has  been  added,  a  final  vigorous  agitation  reduces 
the  larger  lumps  to  fine  grains  which  quickly  dissolve 
in  the  strong  acid  without  the  necessity  of  additional 
heating. 


//  0   -     /  9*9*; 

CHAPTER  VIII 

Methods  of  Testing  Butter  for  Water 

Numerous  methods  designed  for  the  determination 
of  water,  adapted  for  creamery  use,  have  been  called 
into  existence  by  the  enactment  of  laws  controlling  the 
percentage  of  water  in  butter.  All  methods  are  based 
upon  the  same  general  process ;  the  water  is  evapora- 
^  ted  from  a  weighed  portion  of  butter  and  the  amount 
removed  is  then  ascertained  usually  by  weighing  the 
dried  residue,  but  in  some  cases  by  distilling  and 
measuring  the  evaporated  water.  The  apparatus  and 
materials  required  for  any  of  the  methods  can  be  ob- 
tained at  dairy-supply  houses.  The  various  methods 
in  use  differ  in  the  details  and,  before  describing  any 
of  them  we  will  notice  certain  points  of  resemblance 
and  difference,  such  as  relate  to  (i)  preparation  of 
sample,  (2)  weighing  of  sample  and  amount  used, 
(3)  evaporation  of  water,  (4)  ascertaining  the  amount 
of  water  evaporated,  and  (5)  calculation  of  percentage 
of  water  in  butter. 

PREPARATION  OF  SAMPLE 

The  sample  of  butter  must  always  be  taken  and  pre- 
pared with  special  care  (p.  101),  whatever  method  of 
determining  water  is  used.  Unless  the  sample  is  truly 
representative,  the  results  of  testing  are  useless  or 
worse.  When  only  approximate  results  are  desired, 
it  may  answer  the  purpose  to  take  samples  directly 

no 


TESTING  BUTTER  AND  CHEESE  FOR  FAT  III 

from  a  package  of  butter  without  special  preparation 
provided  the  total  amount  used  for  evaporation  is  as 
large  as  50  grams. 

WEIGHING  SAMPLE  AND  AMOUNT  USEI? 

Weighing  should  be  made  only  on  an  accurate  scale 
or  balance  sensitive  to  0.025  gram.  The  vessel  in  which 
the  butter  is  weighed  must  be  clean  and  dry  before 
use.  If  samples  as  large  as  50  grams  are  used,  scales 
sensitive  to  o.i  gram  answer. 

The  amount  of  sample  used  may,  for  convenience,  be 
10  grams  or  some  multiple  of  this.  The  larger  the 
amount  of  samples  used,  the  greater  must  be  the  care 
in  making  evaporation  complete. 

For  careful  work  in  determining  water  in  butter, 
weighing  should  be  done  in  a  suitable  room  especially 
fitted  for  the  purpose;  this  room  should  be  kept  free 
from  dampness  and  dust.  The  scale  or  balance  should 
be  protected  from  dampness,  dust  and,  especially 
when  weighing,  from  drafts  of  air,  which  can  easily  be 
done  by  placing  it  in  a  tightly-made  box  or  case  of 
convenient  size  provided  with  a  door  in  front,  which 
is  kept  closed  when  the  scale  is  not  being  used.  This 
box  can  be  set  on  a  firm  table  or  fastened  securely  to 
the  wall  at  a  convenient  height,  care  being  taken  to 
have  the  scale  exactly  level.  Additional  protection 
from  dampness  is  afforded  by  placing  in  this  box  near 
the  scale  a  teacup  quarter  full  of  strong  sulphuric  acid 
or  dry,  fused  calcium  chloride;  these  substances  ab- 
sorb atmospheric  moisture  and  must  be  replaced  from 
time  to  time  with  fresh  material. 


112  MODERN    METHODS  OF   TESTING   MILK 

EVAPORATION  OF  WATER 

In  the  case  of  all  methods,  the  vessel  containing  the 
weighed  sample  of  butter  is  subjected  to  heat  to  evap- 
orate the  water.  The  means  of  applying  heat  vary; 
in  some  cases,  the  vessel  is  heated  directly  over  an 
alcohol  or  gas  flame,  or  there  may  be  interposed  a 
thin  sheet  of  asbestos  or  iron  plate ;  in  other  methods, 
the  dish  is  placed  in  some  form  of  drying-oven, 
heated  by  steam  under  pressure. 

In  the  process  of  evaporation,  certain  precautions 
must  be  observed,  especially  in  reference  to  (i) 
length  of  time  of  heating,  and  (2)  loss  by  sputtering. 

Length  of  time  of  heating. — This  depends  mainly 
upon  the  size  of  the  sample,  the  degree  of  temperature, 
and  the  diameter  of  the  dish  in  which  the  sample  is 
heated. 

The  objection  to  heating  at  high  temperature  longer 
than  is  necessary  to  evaporate  the  water  completely  is 
that  other  material  is  in  danger  of  being  driven  off 
from  the  butter,  the  consequence  being  that  the  re- 
sults are  too  high.  How  can  we  tell  when  the  water  is 
completely  removed?  This  is,  for  the  most  part,  a 
matter  of  experience.  Generally,  the  appearance  and 
behavior  of  the  dried  residue  are  depended  upon  to 
indicate  when  evaporation  is  complete.  When  butter 
is  heated  in  an  open  dish,  a  foamy,  snow-white  cover- 
ing collects  over  the  surface  as  soon  as  the  butter  be- 
comes quite  hot;  this  white  covering  changes  to  a 
dirty-brown  color,  and  the  crackling  noise  due  to  the 
escape  of  water-vapor  ceases,  after  the  heating  has 
been  continued  some  time,  and  then  a  slightly  pungent 
odor  is  usually  noticeable.  These  conditions  indicate 


METHODS  OF  TESTING  BUTTER  FOR  WATER         113 

that  the  water  has  been  completely  evaporated,  the 
dark  color  and  pungent  odor  showing  that  other  but- 
ter constituents  are  beginning  to  undergo  decomposi- 
tion ;  heating  should  then  cease  at  once.  So  long  as 
any  snow-white  portions  remain,  the  evaporation  is 
not  complete. 

The  escape  of  water-vapor  is  facilitated  by  shaking 
the  dish  with  a  rotary  motion  from  time  to  time  during 
the  evaporation,  thus  breaking  up  the  surface  covering, 
which  tends  to  prevent  the  escape  of  water-vapor. 
Experience  enables  one  quickly  to  detect  the  point  at 
which  heating  should  be  stopped. 

Another  method  of  telling  when  evaporation  is  com- 
plete is  to  hold  the  face  of  a  mirror  over  the  heated 
sample  after  foaming  ceases ;  the  process  is  complete 
when  no  moisture  gathers  on  the  mirror.  Care  must 
be  taken  to  keep  the  mirror  from  becoming  too  warm 
to  condense  water-vapor.  This  may  be  done  by  using 
two  mirrors  alternately,  allowing  one  to  cool  while  the 
other  is  being  used. 

In  the  case  of  samples  heated  in  an  oven,  it  is  well 
to  make  some  experiments.  Remove  the  evaporating 
dish,  when  the  darkening  of  the  residue  appears,  cool 
and  weigh,  after  which  replace  the  dish  in  the  oven 
and  heat  again  for  10  or  15  minutes;  if  the  water 
was  removed  by  the  first  heating,  the  sample  will  weigh 
the  same  as  before,  while  decrease  in  weight  after  the 
second  heating  will  show  that  the  first  heating  was 
insufficient  to  complete  the  evaporation.  A  few  trials 
of  this  kind  will  enable  one  to  tell  very  closely  how 
long  it  will  be  necessary  to  heat  for  complete  evapora- 


114  MODERN    METHODS  OF  TESTING   MILK 

tion  in  the  case  of  samples  of  a  given  weight  and  at  a 
definite  temperature. 

Loss  by  sputtering. — When  butter  is  heated  very 
rapidly,  the  sudden  escape  of  water-vapor  is  liable  to 
cause  sputtering,  throwing  some  of  the  material  out 
of  the  evaporating-dish  and  thus  causing  too  high- re- 
sults. This  is  apt  to  happen  when  the  dish  is  heated 
over  a  high  gas  flame.  The  use  of  an  alcohol  lamp  or 
the  interposition  of  a  piece  of  thin  asbestos  or  iron 
plate  over  the  flame  obviates  this  difficulty.  Sputtering 
may  also  occur  in  a  high-pressure  oven  if  the  temper- 
ature is  too  high  during  the  first  part  of  the  process. 

ASCERTAINING  THE  AMOUNT  OF  WATER 
EVAPORATED 

In  most  methods  the  amount  of  water  evaporated 
is  found  by  subtracting  the  weight  of  the  cooled  dish 
and  contents  after  heating  from  the  weight  of  the  dish 
and  contents  before  heating;  the  weight  lost  during 
heating  represents  the  amount  of  water  in  the  butter. 
The  cooling  and  weighing  should  be  done  in  a  room 
where  the  air  is  'fairly  dry.  In  some  methods,  the 
evaporated  water  is  condensed  in  a  graduated  tube 
and  measured  directly. 

CALCULATION  OF  PERCENTAGE  OF  WATER  IN 
BUTTER 

In  the  case  of  those  methods  which  condense  the 
evaporated  water,  the  percentage  of  water  in  the  butter 
tested  is  read  directly  from  the  graduated  tube.  When 
the  water  is  evaporated  into  the  air  and  its  amount 
determined  by  the  weight  lost,  the  percentage  is  cal- 
culated as  follows:  Divide  the  loss  of  weight  by  the 


METHODS  OF  TESTING  BUTTER  FOR  WATER         115 

weight  of  the  sample  used  and  multiply  the  result  by 
100.  For  example,  a  ic-gram  sample  after  evapora- 
tion of  water  weighs  9  grams ;  the  difference  (i  gram) 
is  the  amount  of  water,  which  is  10  per  cent,  of  the 
butter  sample  tested.  The  arithmetical  operation  is 
indicated  as  follows:  \ 

i  (weight  lost  in  grama)  -f-  10  (amount  of  sample 
in  grams)  x  100  =  10  (thjp^ef  cent,  of  water  in  the 
butter).  In  case  of  a  5O-gram  sample,  which  loses 
7  grams  of  water,  welfare  the  following:  7  -7-50 x- 
100=  14  (the  per  cent,  of  water  in  butter). 

CORNELL  TEST  FOR  WATER   IN   BUTTER 

This  was  devised  by  Ross  at  the  Cornell  University 
experiment  station.  The  apparatus  required  includes 
(i)  an  alcohol  lamp;  (2)  a  cast  aluminum  cup  or 
beaker  for  holding  and  heating  sample.  (A  conve- 
nient size  for  this  and  similar  tests  is  about  3  inches 
high  and  2  inches  in  diameter);  (3)  an  iron  stand; 
(4)  a  thin  sheet  of  asbestos;  (5)  a  hand-clamp  for 
lifting  the  cup.  While  any  balance  or  scale  of  sufficient 
delicacy  can  be  used,  Ross  recommends  as  most  con- 
venient a  special  form  (Fig.  31  a,  p.  79)  which  en- 
ables one  to  calculate  the  results  on  the  arm  of  the 
scale;  this  scale  is  well  adapted  for  cream-testing  also. 
The  distinctive  feature  of  this  method  is  mainly  the 
use  of  asbestos  between  the  dish  and  flame. 

The  operation  is  carried  out  as  follows :  The  sample 
of  butter  (20  grams)  properly  prepared  (p.  101)  is 
weighed  into  the  clean,  dry  aluminum  cup,  the  weight 
of  which  has  already  been  found.  The  alcohol  lamp  is 


Il6  MODERN   METHODS  OF  TESTING   MILK 

placed  under  the  .asbestos  sheet,  which  rests  on  the 
iron  stand.  The  cup  with  the  weighed  sample  in  it  is 
placed  on  the  asbestos  with  the  lifter  and  allowed  to 
remain  until  the  foamy,  snow-white  covering  that  is 
soon  formed  changes  to  a  dirty-brown  color,  which 
is  usually  accompanied  by  a  slightly  pungent  odor. 
The  dish  is  at  once  removed  from  the  asbestos,  allowed 
to  cool  to  room  temperature  and  weighed.  The  per- 
centage of  water  in  the  butter  tested  is  calculated  as 
already  described  (p.  115). 

While  the  sample  is  being  heated,  it  should  be  shaken 
from  time  to  time  with  a  rotary  motion  in  order  to 
break  up  the  surface  covering  and  facilitate  the  escape 
of  the  water-vapor.  So  long  as  snow-white  portions 
remain,  the  evaporation  is  not  complete. 

When  the  special  form  of  scale  that  is  recommended 
is  used,  a  sample  weighing  20.2  grams  is  taken,  which 
permits  direct  reading  on  the  scale-arm  of  the  per- 
centage of  water  in  butter. 

The  Cornell  method  possesses  the  advantages  of 
simplicity,  ease  of  operation  and  reasonable  accuracy ; 
the  apparatus  is  inexpensive  and  durable. 

The  Ames  method,  devised  by  McKay  and  Bower  at 
the  Iowa  experiment  station,  differs  from  the  Cornell 
method  mainly  in  that  the  dish  containing  the  sample 
of  butter  is  heated  over  melted  paraffin  at  a  tempera- 
ture of  about  175°  F.  This  permits  good  control  of 
temperature  and  yields  good  results.  Some  find  the 
use  of  a  paraffin  bath  objectionable  on  account  of 
possible  danger  of  catching  fire.  Paraffin  that  has 
been  repeatedly  heated  is  apt  to  undergo  some  decom- 
position and  give  off  an  unpleasant  odor. 


METHODS  OF  TESTING  BUTTER  FOR  WATER        1 1/ 


WISCONSIN    MOISTURE   TESTS 

At  the  Wisconsin  Experiment  Station,  two  forms 
of  heating  apparatus  have  been  devised.     In  the  Ben- 
kendorf  test  (Fig.  37)  the  special  device  consists  of 
a    small    oven-like   casting 
with  an  open  space  to  re- 
ceive the  evaporating-dish ; 
in  the  bottom  is  placed  a 
thin  sheet  or  mat  of  asbes- 
tos.    It  can  be  heated  by 
alcohol  or  gas.    The  evapo- 
rating-dish is  shallow,  flat- 
bottomed  and  made  of  tin 
or  aluminum,  3  inches  in 
diameter  and  ^  inch  deep. 
The  iron  walls  conduct  the 
heat  to   all   sides   and  the , 
sample  is  uniformly  heated 
throughout,    thus    prevent- 
ing foaming  and  sputtering. 
With    lo-gram   samples,  it 

is  stated  that  at  300°  F.  the  water  can  be  evaporated 
in  about  5  minutes  if  the  plate  is  hot  when  the  sample 
is  placed  on  it.  A  hole  is  provided  for  the  insertion 
of  a  thermometer  so  that  the  exact  temperature  of 
the  oven  may  be  known. 

In  the  Farrington  or  Wisconsin  high-pressure  oven 
(Fig.  37a),  evaporation  of  water  takes  place  at  a  tem- 
perature of  240°  to  280°  F.  It  consists  of  an  iron  oven 
with  double  walls  between  which  steam  enters  under 
pressure  of  60  to  80  pounds.  The  evaporating  dishes 
are  the  same  as  those  used  in  the  Benkendorf  oven, 


FIG.  37 — BENKENDORF  OVEN 


MODERN    METHODS  OF  TESTING   MILK 


four  of  which  can  be  placed  in  the  oven  at  the  same 
time.  The  samples  are  heated  until  the  residue  appears 
brown,  which  takes  from  30  to  60  minutes,  depending 
on  the  amount  of  the  sample  and  the  temperature  of 
the  oven.  A  lo-gram  sample  can  be  dried  at  260°  F. 
in  about  30  minutes;  a  5o-gram  sample  requires  at 
least  60  minutes.  It  is  a  safe  precaution  to  heat  sam- 
ples a  second  time  to  make  sure  that  the  water  is  com- 
pletely evaporated,  especially  until  one  has  had  suffi- 


FIG.  370 — FARRINGTON'S  HIGH-PRESSURE  OVEN 


METHODS  OF  TESTING  BUTTER  FOR  WATER 


eient  experience  to  become  familiar  with  the  best  work- 
ing conditions. 

In  respect  to  accuracy,  the  results  are  satisfactory 
for  creamery  work,  though  some  careful  work  indi- 
cates a  tendency  to  high  results,  owing  to  sputtering 
and  to  decomposition  of  the  butter  at  the  high  tem- 
perature used. 

The  apparatus  has  the  following  advantages:  (i) 
It  is  well  adapted  to  use  in  creameries  because  the 
heat  is  furnished  by  steam  and  the  oven  can  be  directly 
connected  with  the  boiler,  thus  lessening  danger  from 
accidents  by  fire  in  comparison  with  the  use  of  alcohol 
lamps.  (2)  The  process  does  not  require  close  atten- 
tion during  the  evaporation,  when  once  the  operator 
becomes  familiar  with  the  management  of  the  oven. 
(3)  The  temperature  can  be  kept  under  control. 

In  this  connection  we  mention  the  oven  described  by 
Dean  (Dairy  School  at  Guelph,  Ontario,  Can.),  which 
is  a  steam-oven  made  of  galvanized  iron  and  able  to 
withstand  a  pressure  of  10  pounds.  Complete  evapora- 
tion requires  5  or  6  hours. 

PATRICK  AND  IRISH  MOISTURE-TESTS 

These  two  methods  are  essentially  alike.  An  alumi- 
num cup  containing  the  sample  of  butter  is  held  by  a 
hand-clamp  directly  over  the  flame  of  an  alcohol  lamp 
or  gas-burner.  In  the  test  of  Irish,  a  mirror  is  used 
to  ascertain  when  the  water  is  all  evaporated,  which 
calls  for  certain  precautions  (p.  113). 

These  two  tests  are  rapid  but  usually  give  high  re- 
sults, though  not  enough  so  to  make  them  unsuitable 
for  ordinary  work.  In  order  to  obtain  reasonably  ac- 


I2O  MODERN   METHODS  OF  TESTING   MILK 

curate  results,  the  following  precautions  should  be 
observed:  (i)  The  cup  should  be  heated  gradually, 
since  too  rapid  heating  causes  sputtering  and  loss.  (2) 
During  the  evaporation,  the  dish  should  be  shaken 
with  a  rotary  motion  in  order  to  distribute  the  heat 
more  uniformly  and  facilitate  escape  of  water-vapor. 
(3)  The  butter  must  not  be  heated  so  high  nor  so  long 
as  to  cause  decomposition  and  volatilization  of  the 
butter-solids. 

GRAY'S  TEST  FOR  WATER  IN  BUTTER 

This  method  was  worked  out  in  the  Dairy  Division 
of  the  Bureau  of  Animal  Industry,  U.  S.  Dept.  of 
Agr.  (Circular  No.  100).  It  differs  from  the  methods 
already  described  in  several  respects:  (i)  The  water 
is  evaporated  from  the  butter  in  the  presence  of  a 
slightly  volatile  mixture  of  high  boiling-point,  which 
does  not  mix  with  water.  (2)  The  evaporated  water 
is  recovered  by  distillation.  (3)  The  distilled  water 
is  caught  in  a  graduated  tube,  which  permits  direct 
reading  of  the  results  in  percentage  of  water  in 
butter. 

The  apparatus  and  reagents  employed  in  the  test, 
aside  from  an  accurate  scale  with  a  5-gram  and  a  10- 
gram  weight,  an  alcohol  lamp  and  a  6-cc.  measuring- 
graduate  are  (i)  the  special  testing-apparatus,  (2) 
parchment  paper,  perfectly  dry,  (5  by  5  inches  in  size), 
(3)  rubber  stoppers  (one  stopper  lasts  for  about  100 
tests),  and  (4)  the  amyl  reagents  (a  mixture  of  5 
parts  of  amyl  acetate  and  i  part  of  amyl  valerianate, 
entirely  free  from  water-soluble  impurities). 

The  special  testing  apparatus  includes  three  essen- 


METHODS  OF  TESTING  BUTTER  FOR  WATER        121 

tial  pieces  (i)  a  flask  (A,  Fig.37b),  (2)  a  receiving- 
bulb  with  graduated  tube  (C,  Fig.  37b),  and  (3)  a 
condensing-jacket  (E,  Fig.  37b).  The  receiving-bulb 
is  connected  with  flask  A  by  means  of  a  rubber  stop- 
per (B).  G  is  a  ground  glass  stopper  fitting  tightly 
into  the  tube  above  the  graduated  scale.  When  more 
than  one  apparatus  is  usecj,  each  stopper  and  tube 
should  be  properly  marked  so  that  each  stopper  shall 
always  be  used  with  its  corresponding  tube.  Each 
mark  of  the  graduated-scale  represents  0.2  per  cent, 
of  water  when  a  lo-gram  sample  of  butter  is  used. 
The  glass  condensing-jacket  (E,  Fig.  37b)  is  con- 
nected to  the  graduated  tube  by  a  rubber  stopper 
(D,  Fig.  37b). 

The  operation  of  the  test  is  carried  out  as  follows : 
(i)  Weigh  a  lo-gram  sample  by  placing  on  each  scale- 
pan  one  sheet  of  parchment  paper  and  balancing; 
the  sample  is  placed  in  center  of  paper  on  one  pan,  a 
lo-gram  weight  being  in  the  other.  (2)  The  paper 
with  sample  is  folded  in  such  shape  as  to  slip  without 
loss  into  flask  A  (which  must  always  be  clean  and 
dry  before  use).  Some  prefer  to  weigh  the  sample 
of  butter  directly  into  the  flask.  (3)  Then  pour 
6  cc.  of  amyl  reagent  into  flask  A,  (4)  connect  the  ap- 
paratus (which  must  be  clean  and  dry  always  before 
use)  in  the  manner  shown  in  Fig.  37b,  fill  the  condens- 
ing-jacket with  cool  water  to  within  i  inch  of  top 
(F,  Fig.  37b)  and  remove  the  glass  stopper  (to  pre- 
vent danger  of  bursting  of  tube  by  pressure  of  un- 
condensed  water- vapor).  (5)  Then  heat  the  bottom 
A  over  the  flame  of  the  burner.  The  butter 
lelts,  mixes  with  amyl  reagent,  and  later  passes 


122  MODERN   METHODS  OF  TESTING   MILK 

as  vapor  into  the  graduated  tube,  where  it  is  con- 
densed, and  then  runs  back  into  the  receiving-bulb 
(C).  The  condensation  in  the  graduated  part  of  the 
tube  must  be  carefully  watched  and  the  steam  not 
allowed  to  go  higher  than  the  15  cc.  mark,  in  order 
to  avoid  risk  of  losing  water.  If  it  goes  above  this 
mark,  remove  the  flask  from  the  flame  for  a  short  time. 
If  the  mixture  in  flask  A  shows  a  tendency  to  foam 
over,  remove  the  flame.  In  case  of  persistent  foam- 
ing, cool  the  flask  and  contents,  add  about  2  cc.  more 
of  amyl  reagent  and  continue  heating.  When  the  mix- 
ture in  the  flask  becomes  brown  and  all  crackling 
noise  ceases,  the  water  has  all  been  driven  from  the 
flask.  This  usually  requires  5  to  8  minutes.  (6) 
After  completing  distillation,  flask  A  is  disconnected 
from  stopper  B  and  the  glass  stopper  G  is  firmly  in- 
serted in  end  of  graduated  tube.  (7)  The  tube  is 
then  inverted,  transferring  the  water  from  the  receiv- 
ing-bulb (C)  into  the  graduated  tube,  care  being 
taken  not  to  allow  any  water  to  be  lost  through  the 
small  bent  tube  inside  the  bulb.  The  water  is  then 
poured  from  the  condensing- jacket,  after  which  the 
jacket  may  be  removed.  (8)  Some  amyl  reagent  is 
distilled  with  the  water,  but  is  easily  separated  as  fol- 
lows: Hold  the  receiving-bulb  in  the  palm  of  the 
hand  and  the  stoppered  end  away  from  the  body; 
then  raise  to  a  horizontal  position  and  swing  at  arm's 
length  sharply  downward  to  the  side.  This  is  re- 
peated several  times  until  the  line  of  separation  be- 
tween the  water  and  amyl  reagent  is  sharply  distinct, 
the  amyl  reagent  rising  above  the  water.  The  tube 
should  then  be  held  a  short  time  with  the  sto4 


he  tube 

** 


METHODS  OF  TESTING  BUTTER  FOR  WATER         123 


end  downward  and  the  amyl  reagent 
in  the  bulb  agitated  in  order  to  rinse 
down  any  water  adhering  to  the  sides 
of  the  bulb.  (9)  After  cooling  the 
tube  and  contents  the  percentage  of 
water  is  read  directly  from  the  scale, 
when  a  lo-gram  sample  is  used.  The 
water  is  in  the  lower  part  of  the  tube. 
The  reading  is  made  to  the  lower  part 
of  the  meniscus.  When  any  amount 
of  butter  other  than  10  grams  is  used, 
a  corresponding  correction  must  be 
made. 

The  accuracy  of  the  results  obtained 
by  the  Gray  method  depends  upon 
several  factors,  chief  of  which  are  the 
following:  (i)  The  graduation  must 
be  correct.  (2)  The  amyl  reagent 
must  be  pure.  (3)  The  manipulation 
as  described  must  be  followed  strictly, 
(a)  Too  rapid  heating  must  be  avoided 
in  order  to  avoid  the  danger  of  driv- 
ing water-vapor  into  the  air  from  the 
upper  end  of  the  condensing-tube.  (b) 
The  rubber  stopper  B  (Fig.  3/b)  must 
fit  the  neck  of  flask  A  perfectly  and 
must  be  free  from  cracks.  A  loose- 
fitting  stopper  may  allow  loss  of  water 
either  by  escaping  into  the  air  or  by  FIG.  3;b 
collecting  between  the  neck  of  the  flask  GRAY's  APPARATUS 
and^  the  stopper.  Repeated  heating  ™ 
causes  the  rubber  stoppers  to  crack  IN  BUTTER. 


124  MODERN    METHODS   OF   TESTING    MILK 

and  they  are  then  liable  to  collect  and  retain  water  in 
the  cracks ;  this  trouble  may  be  remedied  to  some  ex- 
tent by  rubbing  the  stopper  thoroughly  with  amyl  re- 
agent before  use  each  time,  (c)  The  sample  must  be 
heated  long  enough  to  remove  all  water  not  only  from 
the  butter  but  from  the  flasks  as  well.  Comparative 
tests  reported  by  some  workers  indicate  that  more 
accurate  results  are  obtained  by  heating  the  butter 
until  black  or  nearly  so. 

One  serious  objection  to  the  apparatus  is  that  it  is 
easily  broken.  This  objectionable  feature  has  been 
obviated  in  the  Mitchell- Walker  test  (Eastern  Dairy 
School,  Kingston,  Ontario,  Can.),  which  utilizes  es- 
sentially the  principle  of  the  Gray  test;  most  of  the 
parts  are  of  metal  and  the  manipulation  is  compara- 
tively simple. 


CHAPTER   IX 

Methods  of  Testing  Butter  for  Salt 

All  methods  for  the  determination  of  salt  are  based 
upon  one  principle.  When  a  solution  of  silver  nitrate 
and  a  solution  of  common  salt  (sodium  chloride)  are 
brought  together,  a  chemical  reaction  takes  place,  by 
which  the  silver  combines  with  the  chlorine,  forming 
silver  chloride,  which  is  a  white  precipitate  or  solid 
substance,  t  Moreover,  a  given  amount  of  silver  always 
combines  with  a  definite  amount  of  chlorine.  If,  there- 
fore, to  a  solution  containing  salt,  we  add  a  silver  ni- 
trate solution  of  known  strength  until  the  chlorine  of 
the  salt  is  all  changed  intcfcthe  solid,  white  silver  chlo- 
ride, we  can  tell  just  how  much  salt  is  in  the  tested 
solution  by  keeping  a  record  of  the  amount  of  silver 
nitrate  solution  used.  One  part  by  weight  of  salt  re- 
quires for  complete  precipitation  about  2.9  parts  by 
weight  of  silver  nitrate.  The  only  point  of  difficulty 
is  to  know  just  when  the  chloride  is  all  precipitated, 
but  we  have  a  simple,  accurate  way  of  telling  precisely 
when  this  point  is  reached.  A  solution  of  potassium 
chromate  also  forms  a  precipitate  when  treated  with 
silver  nitrate  but  in  this  case  the  solid  substance  (silver 
chromate)  is  deep-red  or  brick-red  in  color.  Further- 
more, if  we  add  silver  nitrate  solution  to  a  solution 
containing  both  chloride  and  chromate,  stirring  or 
shaking  vigorously  during  the  addition,  the  chloride 

125 


126  MODERN   METHODS  OF  TESTING  MILK 

will  all  be  precipitated  in  the  form  of  the  white  silver 
chloride  before  the  brick-red  silver  chromate  forms 
permanently. 

How  are  the  foregoing  facts  applied  in  finding  the 
percentage  of  salt  in  a  solution?  For  simplicity,  we 
will  use  the  following  illustration  experiments:  Dis- 
solve 29.06  grams  of  pure  silver  nitrate  in  pure  water 
and  then  add  enough  more  water  to  make  just  1000 
cc.  of  solution.  (Standard  silver  nitrate  solutions  are 
best  obtained  ready-made  from  a  reliable  chemical-sup- 
ply house.)  One  cubic  centimeter  of  this  solution  is 
just  equal  to  o.oi  gram  of  salt.  Next  dissolve  2  grams 
of  salt  in  pure  water  to  make  100  cc.  of  salt  solution. 
In  a  cup  or  beaker  measure  10  cc.  of  this  salt  solution 
and  add  2  or  3  drops  of  a  solution  of  potassium  chro- 
mate (made  by  dissolving  as  much  potassium  chro- 
mate as  possible  in  100  cc.  of  cold  water)  ;  then  add 
slowly  from  a  burette  some  of  the  silver  nitrate  solu- 
tion and  stir  or  shake  the  mixture  in  the  cup.  On  the 
first  addition  of  silver  nitrate,  the  mixture  becomes 
turbid  from  the  formation  of  silver  chloride  and  on 
further  addition  sooner  or  later  there  will  appear  a 
deep  brick-red  or  blood-red  coloration  due  to  the  for- 
mation of  silver  chromate.  So  long  as  any  chloride  is 
left  in  solution  in  the  mixture,  the  red  silver  chromate 
will  disappear  on  agitation.  When  the  red  color  begins 
to  become  prominent,  then  run  in  only  o.i  cc.  of  silver 
nitrate  at  a  time,  agitating  vigorously  after  each  addi- 
tion and  continue  until  a  faint  reddish  tinge  colors  the 
whole  mixture  and  does  not  disappear  on  agitation. 
The  color  change  can  best  be  seen  on  a  white  back- 
ground as  in  a  white  cup  or  a  glass  beaker  set  on  white 


METHODS   OF   TESTING    MILK    FOR   SALT  I2/ 

paper.  This  means  that  the  chloride  has  all  become 
precipitated  or  changed  to  solid  silver  chloride,  and 
that  silver  chromate  is  formed  and  remains  in  the  mix- 
ture. When  this  point  is  reached,  add  no  more  silver 
solution.  Examine  the  burette  and  read  the  number 
of  cubic  centimeters  of  silver  nitrate  solution  that  has 
been  used.  Suppose  we  findv  we  have  used  20  cc. ; 
this  means  that  the  10  cc.  solution  tested  contains  0.20 
gram  of  salt,  since  i  cc.  of  silver  solution  precipitates 
the  chlorine  in  o.oi  gram  of  salt.  This  is  equal  to 
about  2  per  cent,  of  salt  in  the  solution. 

Several  applications  have  been  made  for  the  deter- 
mination of  salt  in  butter,  the  difference  in  methods 
being  the  preparation  of  sample,  strength  of  silver 
solution  and  amount  of  material  taken  for  testing. 
At  one  time  silver  nitrate  tablets  were  on  the  market. 

It  will  probably  be  found  best  to  purchase  the  silver 
nitrate  solution  from  some  reliable  chemical-supply 
house.  When,  however,  the  solution  is  made  at  home 
from  silver  nitrate  crystals  purchased  at  .a  .drug-store, 
only  the  pure  compound  should  be  used.  In  dissolv- 
ing silver  nitrate  in  water,  it  is  best  to  use  distilled 
water  or  rain-water.  Water  which  produces  any 
marked  turbidity  when  treated  with  a  few  drops  of 
silver  nitrate  solution  should  not  be  used  in  preparing 
silver  nitrate  solutions. 

\yPERKINS  TEST  FOR  SALT  IN  BUTTER 

This  was  devised  at  the  Ohio  experiment  station 
and  can  be  carried  out  more  quickly  than  other 
methods. 

The  solutions  used  are:   (i)   A  solution  of  silver 


128  MODERN    METHODS  OF   TESTING   MILK 

nitrate  containing  29.06  grams  per  liter;  (2)  commer- 
cial acetone  (or  equal  parts  of  denatured  alcohol  and 
ordinary  ether)  ;  (3)  saturated  water  solution  of  potas- 
sium chromate.  The  apparatus  required  is  a  50  cc. 
burette,  accurately  graduated  to  o.i  cc.,  together  with 
a  white  cup  or  beaker. 

The  operation  of  the  test  is  performed  as  follows: 
Weigh  in  a  cup  or  beaker  5  or  10  grams  of  butter  from 
a  sample  prepared  as  previously  directed  (p.  101). 
Warm  gently  until  just  melted  and  then  add  20  or 
30  cc.  of  commercial  acetone  (obtainable  at  any  good 
drug-store)  or,  if  acetone  is  not  easily  obtainable,  use 
the  mixture  of  denatured  alcohol  and  ether;  add  about 
i  cc.  of  the  chromate  solution,  and  then  run  in  slowly 
from  the  burette  the  solution  of  silver  nitrate,  vigor- 
ously stirring  or  shaking  the  mixture.  Continue  to 
add  the  silver  solution  until  the  brick-red  color  remains 
permanent  for  a  minute  or  more  after  thorough  agita- 
tion. Each  cubic  centimeter  of  silver  nitrate  solution 
used  represents  o.i  per  cent,  of  salt  in  the  butter  when 
a  lo-gram  sample  of  butter  is  taken,  and  0.2  per  cent, 
with  a  5-gram  sample.  For  example,  if  25  cc.  are 
used,  the  result  would  be  2.5  per  cent,  of  salt  in  the 
butter  when  a  lo-gram  sample  is  taken. 

This  test  can  be  applied  in  connection  with  the  de- 
termination of  water  by  most  methods.  Thus,  the 
dried  residue  obtained  with  the  Cornell,  Wisconsin, 
Ames,  Patrick  and  similar  methods  can  be  used  for 
salt  determination  by  adding  a  small  amount  of  water 
and  carrying  out  the  operation  described  in  the  pre- 
ceding paragraph. 


METHODS   OF   TESTING    MILK    FOR   SALT  1 29 

SHAW  TEST  FOR  SALT  IN  BUTTER 

This  test  is  carried  out  in  connection  with  Shaw's 
method  for  determining  fat  in  butter  (p.  103). 

The  solutions  are  a  silver  nitrate  solution  containing 
14.525  grams  of  pure  silver  nitrate  per  liter  (just  one- 
half  the  strength  used  in  the  Perkins  test)  and  a  10  per 
cent,  solution  of  potassium  cjiromate.  Besides  the 
50  cc.  burette  and  a  beaker  or  white  cup,  as  in  the  Per- 
kins test,  there  are  required  a  volumetric  flash  with  a 
250  cc.  mark  and  a  25  cc.  pipette. 

To  determine  the  percentage  of  salt  in  butter  in  con- 
nection with  that  of  fat,  a  solution  of  the  salt  con- 
tained in  the  butter  is  obtained  in  the  manner  described 
in  paragraph  4  (p.  106),  the  wash-water  being  al- 
lowed to  run  into  the  250  cc.  flask  and  the  operations 
in  paragraph  4  are  performed  three  times  instead  of 
once,  the  wash-water  each  time  being  run  into  the 
flask. 

When  the  washings  have  become  cool,  the  flask  is 
filled  to  the  mark  with  cold  water  and  shaken  until  the 
contents  are  well  mixed.  Then  measure  with  the  pi- 
pette 25  cc.  of  the  wash-water  (representing  2  grams 
of  the  original  sample  or  one-tenth  of  20  grams)  into 
the  cup  or  beaker,  add  2  or  3  drops  of  chromate  solu- 
tion and  then  run  into  the  mixture  from  the  burette ' 
the  silver  nitrate  solution,  stirring  constantly,  until  the 
permanent  reddish  tinge  .appears. 

The  silver  nitrate  is  of  such  strength  that  I  cc.  re- 
presents 0.005  grams  (or  0.5  per  cent.)  of  salt  in  but- 
ter when  a  i-gram  portion  is  used,  0.25  per  cent,  where 
a  2-gram  portion  is  taken,  etc.  In  the  foregoing  des- 
cription, 2  grams  are  represented  and  we,  therefore, 


I3O  MODERN    METHODS  OF   TESTING    MILK 

obtain  the  percentage  of  salt  in  the  original  sample  by 
dividing  the  number  of  cubic  centimeters  of  silver 
nitrate  solution  used  by  4.  For  example,  if  the  bu- 
rette reading  shows  that  10  cc.  of  the  silver  solution 
are  used,  then  10  divided  by  4  equals  2.50,  which  is 
the  percentage  of  salt  in  the  sample  of  butter  tested. 

WISCONSIN  TEST   FOR   SALT   IN   BUTTER 

Sammis  adapts  the  general  method  to  creamery  use 
as  follows:  Dissolve  5.1  grams  of  pure  silver  nitrate 
in  pure  water  to  make  250  cc.  of  solution.  Each  cubic 
centimeter  of  this  solution  represents  i  per  cent,  of 
salt  when  we  use  17.6  cc.  of  the  wash- water,  which  is 
obtained  by  shaking  10  grams  of  butter  with  250  cc. 
of  clean,  warm  water.  The  test  is  then  carried  out  in 
the  manner  described  in  connection  with  the  preceding 
tests. 


CHAPTER  X 

Methods  of  Testing  the  Acidity  of  Milk  and  Milk 
Products 

It  is  often  necessary  to  know  how  much  acid  is 
present  in  milk,  cream,  whey,  etc.  The  amount  of 
acid  in  milk  may  be  a  suggestive  indication  of  the 
age  of  milk  and  of  its  care.  In  butter-making,  the 
uniformity  of  the  product  depends  largely  upon  the 
ripening  of  cream,  which  can  be  well  controlled  only 
by  knowing  its  acidity.  In  cheese-making,  it  is  at 
times  important  to  know  whether  milk  contains  too 
much  acid  and  it  is  also  quite  essential  to  have  some 
knowledge  of  the  amount  of  acid  present  in  the  milk 
and  whey  at  different  stages  of  the  operation. 

THE   CAUSES    OF   ACIDITY    IN    MILK   AND    ITS 
PRODUCTS 

We  may  distinguish  two  kinds  of  acidity  in  milk 
and  its  products:  (i)  Apparent  acidity,  and  (2)  acid- 
ity due  to  lactic  acid.  The  apparent  acidity  is  due  to 
the  presence  in  normal  milk  of  casein  and  acid  phos- 
phates, which  have  the  power,  like  free  acids,  of  neu- 
tralizing alkalis.  This  apparent  acidity  in  fresh  milk 
is  about  .07  or  .08  per  cent,  on  the  average.  It  varies 
with  different  conditions,  increasing,  for  instance,  with 
advance  of  lactation. 

Acidity  due  to  lactic  acid  is  formed  in  milk  after  it 
is  drawn,  and  is  caused  by  the  action  of  certain  forms 

131 


132  MODERN   METHODS  OF  TESTING   MILK 

of  bacteria  upon  milk-sugar.  In  general,  when  milk 
contains  over  .10  per  cent,  of  acid,  it  may  safely  be 
assumed  that  it  contains  some  lactic  acid.  The  amount 
of  lactic  acid  present  in  milk  may  be  approximately 
found  by  subtracting  .10  from  the  total  amount  of 
acid  apparently  present.  However,  in  speaking  of  the 
acidity  of  milk,  we  usually  mean  the  total  acidity,  and 
not  that  due  to  lactic  acid  alone.  One  can  not  com- 
monly detect  a  sour  taste  in  milk  that  has  a  total  acidity 
under  .3  per  cent. 

GENERAL  PRINCIPLES  OF  TESTING  ACIDITY 

The  method  of  determining  the  amount  of  acid  in 
milk  and  its  products  is  based  upon  the  well-known 
chemical  action  taking  place  between  acids  and  alka- 
lis. Whenever  we  bring  together  in  solution  an  acid 
and  an  alkali,  they  combine  with  each  other  and  form 
a  third  compound,  the  acid  and  alkali  disappearing  as 
such.  The  acid  and  alkali  are  said  to  neutralize  each 
other  and  the  process  is  called  neutralization.  For 
example,  if  we  add  together  some  hydrochloric  (muri- 
atic) acid  and  sodium  hydroxide  (caustic  soda)  in 
right  proportions,  we  shall  have  neither  hydrochloric 
acid  nor  caustic  soda,  but  a  new  compound,  sodium 
chloride  (common  salt),  which  has  been  formed  by 
the  action  of  the  acid  and  alkali  upon  each  other.  The 
hydrochloric  acid  used  in  the  experiment  tastes  sour 
and  biting,  while  the  caustic  soda  solution  has  a  pecu- 
liar odor,  feels  soapy  on  the  skin,  and,  if  strong  enough, 
destroys  the  skin.  After  these  two  compounds  are 
brought  together  in  proper  proportions,  there  is  no 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      133 

longer  observed  any  sour  taste  of  acid  or  soapy  feel- 
ing or  odor  of  alkali,  because  the  acid  and  alkali  have 
neutralized  each  other  and  have  combined  to  form 
simply  common  salt,  the  presence  of  which  is  noticed 
by  its  taste.  The  solution  is  said  to  be  neither  alkaline 
nor  acid,  but  neutral. 

USE  OF  INDICATORS  IN  TESTING  ACIDITY 

In  working  with  acids  and  alkalis,  it  is  necessary 
to  have  some  simple  means  of  knowing  when  a  solu- 
tion is  acid,  alkaline  or  neutral  (neither  acid  nor  alka- 
line). This  can  be  found  by  using  some  substance, 
called  an  indicator,  which  is  so  acted  on  by  alkalis 
and  acids  as  to  undergo  changes  of  color,  being 
changed  one  color  by  alkalis  and  a  different  color 
by  acids.  One  substance  which  finds  wide  use  as  an 
indicator  is  a  chemical  compound  called  phenolphthal- 
ein,  a  solution  of  which  is  turned  pink  by  alkalis  and 
colorless  by  acids.  For  use  in  testing  acidity,  one  dis- 
solves 10  grams  of  the  dry  powder  in  300  cc.  of  90 
per  cent,  alcohol,  or  5  grams  in  100  cc.  of  50  per  cent, 
alcohol,  adding  one  or  more  drops  of  dilute  alkali  until 
the  solution  is  slightly  pinkish  in  color.  It  is  necessary 
to  use  only  5  or  10  drops  of  this  solution  as  indicator. 

GENERAL  APPLICATION  OF  PRINCIPLES  OF 
NEUTRALIZATION 

What  use  can  be  made  of  the  foregoing  facts  in 
finding  the  per  cent,  of  acid  in  a  solution?  For  sim- 
plicity, we  will  use  the  following  illustrative  experi- 
ment :  In  a  glass  or  teacup  we  put  100  cc.  of  a  solu- 
tion containing  .25  per  cent,  of  lactic  acid  and  add  5 
or  10  drops  of  indicator  solution.  Into  this  mixture 


134  MODERN   METHODS  OF  TESTING  MILK 

we  run  from  a  graduated  cylinder  or  burette  some 
standard  solution  of  caustic  soda,  prepared  by  dis- 
solving 4  parts  by  weight  of  pure  caustic  soda  in  1,000 
parts  of  distilled  water.  This  solution  of  caustic  soda 
we  add,  a  little  at  a  time,  to  the  solution  of  lactic 
acid,  stirring  or  otherwise  agitating  the  mixture  thor- 
oughly after  each  addition.  The  pink  color  that  ap- 
pears when  the  caustic  soda  solution  is  added  disap- 
pears on  stirring.  After  the  alkali  has  been  added 
several  times,  the  color  disappears  less  rapidly  each 
time.  The  gradual  addition  of  the  alkali  is  continued 
until  finally  the  pink  color  does  not  disappear  readily 
on  continued  agitation  but  remains  for  some  moments. 
The  neutralization  of  the  acid  by  the  alkali  is  complete, 
and  the  addition  of  alkali  stops  at  this  point.  The  ap- 
pearance of  the  pink  color  throughout  the  body  of  the 
liquid  means  that  enough  alkali  has  been  added  to 
combine  with  the  lactic  acid,  and  a  little  more,  one 
drop  of  the  alkali  solution  being  enough  to  produce 
the  pink  color  with  the  indicator  after  the  acid  is  neu- 
tralized. The  liquid  in  the  cup  contained  at  the  start 
only  a  solution  of  lactic  acid.  As  soon  as  we  added 
alkali,  it  combined  with  the  lactic  acid,  forming  the 
neutral  compound,  sodium  lactate.  We  then  had  a 
mixture  of  lactic  acid  and  sodium  lactate.  As  we  con- 
tinued to  add  alkali,  the  amount  of  sodium  lactate  in- 
creased, while  the  amount  of  lactic  acid  decreased. 
Finally,  a  point  is  reached  when  the  solution  in  the 
cup  contains  no  free  lactic  acid,  but  only  sodium  lac- 
tate, and  the  addition  of  one  more  drop  of  alkali  turns 
the  indicator  pink,  producing  a  more  lasting  coloration 
throughout  the  solution  and  showing  that  the  acid 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      135 

has  been  completely  neutralized,  that  is,  changed  into 
sodium  lactate. 

Having  completed  the  neutralization  of  the  acid, 
we  examine  the  burette  or  the  graduated  cylinder  con- 
taining the  alkali  to  find  exactly  how  much  alkali  so- 
lution has  been  used  in  neutralizing  the  acid.  The 
lactic  acid  has  required,  say,  ,28  cc.  of  soda  solution. 
Each  cubic  centimeter  of  alkali  neutralized  by  acid 
corresponds  to  .009  gram  of  acid,  and  28  cc.  would 
therefore  correspond  to  .25  gram  of  lactic  acid.  This 
amount  of  lactic  acid  in  100  cc.  is  .25  per  cent.  The 
process  of  making  a  chemical  determination  by  means 
of  a  standard  solution  is  known  as  titration. 

NEUTRALIZATION  METHOD  APPLIED  TO  TEST- 
ING ACIDITY  OF  MILK  AND  MILK  PRODUCTS 

In  practical  dairy  work,  one  is  freed  from  the  ne- 
cessity of  preparing  standard  solutions,  except  in  a 
simple  way,  and  the  calculations  needed  to  figure  the 
results  are  direct  and  easy.  The  caustic  soda  solution 
is  prepared  in  such  strength  that  i  cc.  of  it  equals  .1  or 
o.oi  per  cent,  of  lactic  acid,  when  a  certain  amount  of 
milk  or  other  substance  is  used.  All  tests  for  the  acid- 
ity of  milk  and  its  products  are  based  upon  the  gene- 
ral principles  previously  described  and  differ  from  one 
another  simply  in  some  of  the  details  of  carrying  out 
the  process.  There  are  now  available  several  forms 
of  so-called  acid  tests. 

The  essential  apparatus  and  reagents  for  determining 
acidity  in  milk  and  its  products  are  the  following :  ( I ) 
An  accurately  graduated  burette  or  cylinder  for  meas- 
uring the  amount  of  standardized  alkali  solution  used ; 


136  MODERN   METHODS  OF  TESTING   MILK 

(2)  a  pipette  for  measuring  the  amount  of  milk,  cream, 
etc.  to  be  tested;  (3)  a  white  cup  or  glass  beaker  for 
holding  the  milk,  cream,  etc.  during  titration,  that  is, 
while  the  alkali  is  running  into  the  liquid  tested;  (4) 
a  glass  or  gutta-percha  stirring-rod,  with  which  to 
stir  the  mixture  during  the  titration;  (5)  a  standard- 
ized alkali  solution;  (6)  solution  of  phenolphthalein 
in  alcohol  to  indicate  when  the  liquid  tested  becomes 
alkaline  (p.  132).  (7)  a  liter  flask  or  graduate  for 
making  up  alkali  solution.  Some  of  these  essentials 
we  will  consider  in  more  detail. 

The  Burette  should  be  accurately  graduated  and  the 
smallest  divisions  should  be  o.i  cc.  at  least.  The  size 
of  the  burettes  in  use  varies.  A  common  and  conven- 
ient size  is  one  that  holds  50  cc.  When  the  amount 
of  solution  taken  for  testing  is  small  (not  over  9 
grams),  a  10  cc.  burette  can  be  used. 

The  Pipette  most  easily  available  is  the  ordinary 
17.6  cc.  pipette  used  in  milk  testing.  Some  of  the  tests 
use  a  50  cc.  pipette ;  others,  8.8  cc. 

Standardized  alkali  solution, — This  usually  consists 
of  pure  sodium  hydroxide  (caustic  soda)  dissolved  in 
pure  water  (distilled  water  should  always  be  used  if 
possible).  It  must  be  prepared  so  as  to  be  of  exact, 
known  strength.  We  will  consider  this  solution  in  re- 
spect to  (i)  different  strengths  used,  (2)  methods  of 
preparation,  and  (3)  precautions  in  keeping. 

(i)  Different  strengths  used. — The  alkali  solution 
differs  in  strength  in  different  forms  of  tests,  usually 
being  one-tenth  normal  (  -^  )  or  one-fiftieth  normal 
(  -^V  ).  A  tenth-normal  alkali  solution  is  of  such 
strength  that  i  cc.  neutralizes  0.009  gram  of  lactic  acid. 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      137 

If,  therefore,  an  i8-gram  (17.6  cc.)  sample  is  used  for 
testing,  i  cc.  of  tenth-normal  alkali  solution  corre- 
sponds to  0.05  per  cent,  (one-twentieth  of  one  per 
cent.)  of  lactic  acid  in  the  solution  tested;  o.i  cc.  of 
alkali  solution  corresponds  to  0.005  (one  two-hun- 
dredth of  one  per  cent.)  of  acid.  When  a  Q-gram 
sample  is  used,  I  cc.  of  tenth-normal  alkali  solution 
corresponds  to  o.i  per  cent,  (one-tenth  of  one  per 
cent.)  of  lactic  acid  in  the  solution  tested;  and  O.I  per 
cent,  of  alkali  corresponds  to  o.oi  per  cent,  (one  one- 
hundreth  of  one  per  cent.). 

In  a  one-fiftieth  normal  solution,  I  cc.  of  alkali  cor- 
responds to  0.0018  gram  of  lactic  acid.  Therefore, 
in  case  of  an  i8-gram  (17.6  cc.)  test  sample,  I  cc.  of 
such  alkali  solution  corresponds  to  o.oi  per  cent,  (one 
one-hundredth  of  one  per  cent.). 

(2)  Methods  of  preparation. — The  standard  alkali 
solution  is  obtained  in  one  of  several  ways,  (i)  It 
can  be  purchased  ready-made  in  any  strength  desired 
from  dairy-supply  or  chemical-supply  houses.  It  costs 
most  in  this  way.  (2)  The  chemically  pure  dry  sodium 
hydroxide  (caustic  soda)  can  be  purchased  from  re- 
liable chemical-supply  houses  in  exact  amounts  and  dis- 
solved in  water.  This  should  be  the  cheapest  way  of 
obtaining  the  alkali  solution.  For  example,  4  grams 
of  the  pure  compound  dissolved  in  1000  cc.  (i  liter) 
of  water  makes  a  tenth-normal  solution ;  40  grams  dis- 
solved in  1000  cc.  of  water  makes  a  normal  solution ; 
and  100  cc.  of  this  normal  solution,  diluted  to  1000  cc. 
makes  a  tenth-normal  solution  or,  diluted  to  5000  cc. 
makes  a  fiftieth-normal  solution.  (3)  The  normal 
alkali  solution  can  be  purchased  and  made  to  any 


138  MODERN   METHODS  OF  TESTING   MILK 

desired  strength  by  dilution.  (4)  Alkali  tablets  and 
powders  containing  a  definite  amount  of  carbonate 
can  be  purchased  and  dissolved  according  to  directions. 

In  preparing  alkali  solutions,  observe  the  following 
precautions:  (a)  Measuring. — The  measuring-flask  or 
graduated  cylinder  used  in  making  dilutions  must  be 
accurate,  (b)  Water  used  for  dilution. — The  water 
used  must  be  neither  acid  nor  alkaline;  water  care- 
fully distilled  and  kept  free  from  impurities  should 
always  be  used,  if  possible;  next  best  is  clean  rain- 
water, (c)  Use  of  dry  alkali — When  pure  sodium 
hydroxide  (caustic  soda)  is  used,  it  must  be  care- 
fully transferred  without  loss  from  the  bottle  to 
the  vessel  in  which  solution  and  dilution  are  to  take 
place;  the  bottle  is  rinsed  with  water  several  times, 
the  rinsings  being  poured  into  the  vessel  holding 
the  alkali.  The  dissolving  of  caustic  soda  in  water 
produces  heat  and  the  solution  should  be  allowed  to 
cool  to  room  temperature  before  it  is  finally  diluted  to 
the  desired  mark.  Bottles  containing  alkali  in  the  dry 
form  should  come  tightly  sealed,  and  be  kept  so,  and 
should  not  be  opened  until  the  solution  is  to  be  made. 
It  is  necessary  to  use  the  entire  contents  of  the  bottle 
at  one  time,  (d)  Use  of  concentrated  alkali  solution. — 
When  a  normal  alkali  solution  is  purchased  and  di- 
luted, the  same  precautions  must  be  observed  as  when 
the  dry  form  is  used. 

(3)  Precautions  in  keeping  alkali  solution. — The  al- 
kali solution  should  be  kept  from  contact  with  air  in 
order  to  prevent  weakening  by  absorption  of  carbon 
dioxide  and  moisture.  A  weakened  alkali  solution  has 
the  effect  of  giving  higher  results  of  acidity  than  the 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      139 

truth.  Several  forms  of  bottle  have  been  devised 
which  reduce  this  danger  to  a  minimum  ;  some  of  these 
are  illustrated  in  Figs.  39,  3ga  and 


OPERATION  OF  TESTING  FOR  ACIDITY 

Before  describing  details  of  any  of  the  methods  in 
use,  we  will  briefly  consider,  some  of  the  principal 
points  that  apply  to  all  methods.  From  the  material 
to  be  tested  measure  the  amount  desired  into  a  cup 
or  beaker;  nothing  is  better  than  a  white  china  tea- 
cup. The  pipette  is  rinsed  by  filling  it  with  water, 
which  is  added  to  the  material  in  the  cup.  The  addi- 
tion of  water  to  the  sample  to  the  extent  of  three  or 
four  volumes  will  enable  one  to  see  the  pink  coloration 
at  the  end  more  sharply.  Then  add  5  to  10  drops  of  the 
phenolphthalein  solution,  and  from  the  burette  filled 
with  alkali  run  small  portions  into  the  mixture  in  the 
cup,  stirring  thoroughly  after  each  addition.  A  pink 
color  soon  appears  but  disappears  on  stirring.  The 
addition  of  alkali  in  small  amounts  at  a  time  is  con? 
tinued  with  care;  sooner  or  later,  according  to  the 
amount  of  acid  present,  it  will  be  noticed  after  each 
addition  of  alkali,  that  the  pink  color  disappears  more 
slowly  showing  that  the  acid  is  becoming  nearly  neu- 
tralized. When  the  color  disappears  quite  slowly,  add 
the  alkali  not  more  than  one  drop  at  a  time.  Finally, 
a  point  is  reached  when,  after  the  addition  of  one  drop 
of  alkali,  the  pink  color  does  not  disappear  even  after 
stirring  20  to  30  seconds.  This  indicates  that  the  acid 
is  completely  neutralized.  Add  no  more  alkali.  The 
pink  color  will  disappear  after  standing  some  time, 
even  when  the  solution  is  alkaline.  Some  experience 


I4O  MODERN    METHODS   OF  TESTING   MILK 

enables  one  easily  to  know  when  the  pink  color  is 
sufficiently  permanent.  It  is  very  helpful  in  recogniz- 
ing the  point  of  neutralization  to  have  some  color- 
standard  with  which  to  compare  the  pink  color  obtained 
on  neutralization;  it  also  insures  greater  uniformity 
in  results.  For  this  purpose  a  color-standard  can  be 
prepared  in  the  manner  described  on  page  192.  The 
number  of  cubic  centimeters  of  alkali  used  is  then 
read  from  the  burette. 

Calculation  of  results. — The  percentage  of  lactic 
acid  in  the  material  tested  can  be  calculated  from  the 
following  rule :  Multiply  the  number  of  cc.  of  alkali 
used  by  the  amount  of  lactic  acid  neutralized  with  i  cc. 
of  alkali  (0.009  in  case  of  tenth-normal  solutions,  and 
0.0018  in  case  of  fiftieth-normal  solutions)  ;  divide  the 
result  by  the  amount  of  sample  used  in  the  test  (9,  18, 
etc.)  and  multiply  the  last  result  by  100.  This  rule 
may  be  expressed  by  the  following  formula: 


Per  cent,  of  acid  = 

c.c.  alkali  X  acid  equivalent  of  I  c.c.  alkali 
Amount  of  sample  used  for  test 


XIOO 


It  makes  comparatively  little  difference  in  the  results 
whether  the  figure  representing  the  .amount  of  sample 
used  is  given  in  the  form  of  grams  or  cubic  centi- 
meters. The  difference  amounts  to  only  .02  or  0.03  per 
cent,  ordinarily. 

Some  needless  confusion  has  been  introduced  by 
stating  the  results  in  the  form  of  "degree  of  acidity," 
one  degree  meaning  I  cc.  of  tenth-normal  alkali  solu- 
tion neutralized  when  a  certain  amount  of  material  is 
taken  for  testing.  In  the  dairy  literature  of  Europe, 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      14! 

much  confusion  exists  in  this  respect,  the  meaning  of 
a  "degree"  varying  according  to  the  method  used.  It 
seems  highly  desirable  on  all  accounts  always  to  state 
the  results  of  acidity  determination  in  terms  of  per- 
centage of  lactic  acid ;  this  method  now  practically  pre- 
vails in  America.  In  most  of  the  tests  in  common  use, 
no  calculations  or  only  very  simple  ones,  have  to  be 
made,  because  the  amount  of  material  taken  and  the 
strength  of  alkali  used  are  such  as  to  enable  one  to 
read  the  results  in  direct  percentage  from  the  burette, 
as  we  have  already  noticed  (p.  137). 

METHODS  USED  IN  TESTING  ACIDITY 

After  having  considered  the  general  principles  and 
their  application,  we  do  not  need  to  describe  the  dif- 
ferent methods  in  detail  further  than  to  point  out  the 
distinctive  features  of  each,  since  the  really  essential 
features  are  the  same  in  all. 

Van  Norman's  method  (Bulletin  No.  104,  Purdue 
Univ.  Agr.  Exp.  Sta.,  1905)  is  based  upon  the  use  of 
a  fiftieth-normal  solution  of  alkali,  prepared  by  dilut- 
ing 37  cc.  of  normal  solution  of  sodium  hydroxide 
(caustic  soda)  to  1850  cc.  (or  20  cc.  of  normal  solu- 
tion to  1000  cc.),  observing  precautions  already 
pointed  out  (Fig.  38).  The  normal  solution  must  be 
of  guaranteed  accuracy  and  should  be  obtained  only 
from  a  reliable  chemical  or  dairy-supply  house.  The 
amount  of  milk,  cream,  etc.  used  in  testing  is  that  mea- 
sured by  a  17.6  cc.  pipette.  The  alkali  may  be  run  into 
the  cup  containing  the  material  to  be  tested  either  from 
a  burette  or  from  a  100  cc.  graduated  cylinder  until 
the  characteristic  pink  tint  is  obtained  (p.  139). 


142 


MODERN   METHODS  OF  TESTING  MILK 


FIG.    38 — VAN   NORMAN    ACIDITY   TEST 

Each  cubic  centimeter  of  alkali  solution  used  corres- 
ponds to  o.oi  per  cent,  of  acid.  Thus  40  cc.  of  alkali 
solution  equals  .40  per  cent,  of  acid  in  the  material 
tested. 

Farrington's  alkali-tablet  method  (Fig.  38a)  makes 
use  of  tablets  containing  the  alkali  and  indicator  mixed 
together ;  one  tablet  contains  enough  alkali  to  neutralize 
0.035  gram  of  lactic  acid.  When  5  tablets  are  dissolved 
in  97  cc.  of  water,  a  fiftieth  normal  solution  is  fur- 
nished, each  cubic  centimeter  of  which  is  equal  to  o.oi 
per  cent,  of  lactic  acid  when  a  17.6  cc.  sample  of  ma- 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      143 


terial  is  taken  for  the  test.    In  making  the  test,  the  solu- 
tion is  poured  from  a  100  cc.  graduated  cylinder. 

In  preparing  the  alkali  solution,  5  tablets  are  put 
into  the  100  cc.  cylinder  which  is  then  filled  to  the  97 
cc.  mark  with  clean,  soft  water,  preferably  distilled. 
The  cylinder  is  then  tightly  stoppered  and  laid  on  its 

side  until  the  tablets  dis- 
solve, which  requires  seve- 
ral hours.  The  cylinder 
must  be  kept  tightly  stop- 
pered so  that  none  of  the 
solution  can  be  lost  while 
the  tablets  are  dissolving. 
A  slight  flocculent  residue, 
consisting  of  some  inert 
matter  used  in  making  the 
tablets,  will  not  dissolve.  The  solution  should  always 
be  shaken  well  before  using.  When  not  in  use,  it 
should  be  kept  tightly  stoppered.  Solutions  that  have 
been  prepared  longer  than  a  week  may  change  in 
strength  and  it  is  better  to  prepare  fresh  solutions 
than  to  use  old  ones.  The  solid  tablets  do  not  change 
if  kept  dry. 


FIG.  380 — FARRINGTON'S 

ALKALINE-TABLET  TEST 

FOR  ACIDITY 


Spillmaris  Modification  of  Farrington's  Test 

The  apparatus  consists  of  an  ordinary  teacup,  a  reg- 
ular 17.6  cc.  pipette,  a  quart  Mason  fruit- jar,  and 
"Spillman's  .acid-test  cylinder"  (Fig.  38!)).  The  alkali 
solution  is  prepared  by  dissolving  alkaline  tablets  in 
water  at  the  rate  of  5  tablets  for  one  cylinder  of  water 
filled  to  the  mark  8,  the  solution  being  made  and  kept 


144 


MODERN   METHODS   OF  TESTING   MILK 


in  the  fruit- jar.  Observe  the  precautions  given  above 
in  using  tablet  solutions.  In  making  the  test,  put 
17.6  cc.  of  the  material  to  be  tested  in  a  teacup,  pour 
into  the  cup  the  alkali  solution  in  the  manner  described 
above,  until  the  pink  color  remains. 
Then  pour  the  contents  of  the  teacup 
into  the  Spillman  cylinder  and  read 
the  scale  at  the  surface  of  the  liquid 
in  the  cylinder.  The  results  indicate 
the  acidity  in  tenths  of  one  per  cent. 
The  cylinder  reads  as  high  as  8  tenths. 


Alkaline  Tablet  Test  Modified  for  Ra- 
pid Estimation  of  Acidity 


It   is   often    desirable    to   ascertain 
fc    quickly  whether  milk  or  cream  con- 
FIG.  38^       tains  more  or  less  than  .2  or  .3  per 
SPILLMAN'S  ACID-  cent,  of  acid.     Farrington  and  Woll 

TEST  CYLINDER      ,  ,        •        ,     ,,          £    n          .  ,,        , 

have  devised  the  tollowing  method : 
An  alkali  solution  is  prepared  by  dissolving  in  an  8- 
ounce  bottle  2  tablets  for  each  ounce  of  water  used. 
A  No.  10  brass  cartridge  shell,  on  which  a  wire  handle 
is  soldered,  is  used  for  measuring  the  sample  to  be 
tested  and  also  the  alkali.  A  cartridgeful  of  milk  or 
cream  is  placed  in  a  teacup  and  then  a  cartridgeful 
of  the  alkali  solution  is  added.  The  contents  of  the 
cup  are  mixed  by  a  rotary  motion.  If  the  sample 
tested  remains  white,  it  contains  over  .2  per  cent,  of 
acidity ;  if  a  pink  color  remains,  the  acidity  is  less  than 
.2  per  cent.  The  intensity  of  the  pink  color  indicates 
the  relative  amount  of  acid  present,  since  the  color 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      145 


will  be  more  intense  in  proportion  as  there  is  less  acid. 
Any  other  measure  may  be  us£d  in  place  of  the  brass 
cartridge-shell,  but  in  every  case  care  must  be  taken 
to  use  equal  amounts  of  milk  or  cream  and  of  alkali 
solution. 

Publow's  method  (Fig.  39a)  is  fully  described  in 
Circular  No.  7,  Cornell  University  Experiment 
Station,  1909.     The  alkali  solution  is  tenth-nor- 
mal, prepared  by  diluting   50  cc.   of  a   special 
solution   (containing  9.2  grams  of  pure  caustic 
soda)  to  2300  cc.     In  making  the  test  a  9-gram 
sample  is  used,  the  test  being  carried  out  in  the 
usual   way.     The   burette   used 
holds   10  cc.     Each  cubic  centi- 
meter   of    alkali    solution    used 
represents  o.i  per  cent,  of  acid 
in  the  material  tested. 

Marschall's  method  like  Pub- 
low's  uses  a  9~cc.  sample  and  a 
tenth-normal   solution  of  alkali, 
(called     "neutralize!-").         The 
characteristic     feature     of     the    FIG  39_CONVENIENT 
method  is  a  combined  burette  and  APPARATUS  FOR  ACIDITY- 
bottle  for  holding  the  alkali  solu-  TESTING 

tion  (Fig.  39b).  The  burette  is 
graduated  to  0.2  cc.  The  reading  represents  o.i  per 
cent,  of  acid  for  each  cubic  centimeter  of  alkali  solu- 
tion used.  The  alkali  is  also  furnished  in  dry  form  in 
connection  with  this  test,  the  contents  of  one  package 
making  1000  cc.  of  tenth-normal  alkali. 

Manns'  method  uses  a  so-called  "neutralizer,"  which 
is  simply  a  tenth-normal  solution  of  sodium  hydroxide 


146  MODERN   METHODS  OF  TESTING   MILK 


FIG.    3Qa — PUBLOW  S    APPARATUS    FOR    ACIDITY-TESTING 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      147 

(caustic  soda),  a  50  cc.  burette  and  50  cc.  of  the 
sample  to  be  tested.  The  operation  is  carried  out  in 
the  usual  manner  (p.  139).  To  calculate  th§  results 


FIG.   39& — MARSCHALL  APPARATUS   FOR  ACIDITY-TESTING 

into  percentage  of  lactic  acid  in  the  material  tested, 
multiply  the  number  of  cubic  centimeters  of  alkali  used 
by  0.018.  The  method  as  originally  given  is  inconve- 
nient and  much  less  used  than  formerly.  The  cost  of 
transportation  of  so  dilute  a  solution  of  alkali  is  need- 
lessly increased  in  comparison  with  tablets  or  normal 


148  MODERN    METHODS   OF  TESTING   MILK 

solutions  and  the  large  amount  of  material  used  (50 
cc.)  is  not  only  inconvenient  and  time-wasting  but 
calls  for  the  use  of  larger  amounts  of  alkali  than  are 
necessary.  It  is  much  better  to  use  not  more  than  a 
9-gram  sample  and  then  the  reading  can  be  made 
direct ;  each  cubic  centimeter  of  solution  representing 
o.i  per  cent,  of  lactic  acid,  or,  if  a  17.6  cc.  sample  is 
used,  the  reading  is  divided  by  2. 

TESTING  THE  ACIDITY    OF  WHEY 

Whey  may  be  tested  by  any  of  the  methods  de- 
scribed. Owing  to  the  comparatively  low  acidity  of 
whey  in  the  operation  of  cheese-making,  it  is  desirable 
either  to  have  the  alkali  dilute  ( i  cc.  of  alkali  equal  to 
.01  per  cent,  acid),  or  else  to  take  twice  as  much  whey 
for  testing  as  in  the  case  of  cream,  the  final  results 
being  corrected  by  dividing  by  2.  The  whey  should 
be  free  from  particles  of  curd,  since  curd  has  the 
power  of  neutralizing  alkali  to  some  extent.  The  per- 
centage of  acid  in  milk  can  be  used  as  a  guide  in 
ripening  the  milk  before  adding  rennet,  in  the  rate  of 
heating  (cooking)  the  curd,  in  the  regulation  of  the 
piling  of  the  curd,  in  the  time  of  milling,  etc. 

TESTING  THE  ACIDITY  OF  CHEESE 

From  a  sample  of  cheese,  prepared  in  the  manner 
described  on  page  108,  weigh  9  grams  and  to  this 
add  water  at  a  temperature  of  100°  to  110°  F.  until 
the  volume  equals  90  to  100  cc.  Agitate  vigorously 
and  filter.  To  the  filtrate  add  alkali  solution,  each 
cubic  centimeter  of  which  equals  .01  per  cent,  of  lac- 
tic acid,  carrying  out  the  test  as  with  milk,  cream,  etc. 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      149 

The  number  of  cubic  centimeters  of  alkali  used,  mul- 
tiplied by  2,  equals  the  per  cent,  of  acid  in  the  cheese. 
Much  higher  results  are  obtained  if  one  treats  the 
cheese  instead  of  its  water  extract  with  alkali,  because 
the  nitrogen  compounds  of  the  cheese  neutralize  alkali. 

RELATION  OF  FAT  IN  CREAM  TO  ACIDITY  OF 
CREAM-RIPENING 

Cream  rich  in  fat  ripens,  that  is,  becomes  acid,  more 
slowly  than  cream  poor  in  fat.  This  is  so,  because  the 
larger  the  percentage  of  fat  in  cream  the  smaller  is 
the  percentage  of  sugar,  and  the  sugar  is  the  source  of 
lactic  acid.  The  favorable  influence  of  ripening  upon 
the  process  of  churning  is  believed  to  be  due  to  the 
action  of  the  acid  upon  the  calcium  casein  of  the  cream, 
converting  it  into  calcium  lactate  and  so  lessening  its 
tenacious  hold  upon  the  fat-globules  in  emulsion.  The 
fat  itself  of  the  cream  is  not  changed.  The  amount 
of  acid  to  be  formed  in  cream-ripening  is,  therefore,  to 
be  governed  more  by  the  amount  of  calcium  casein  in 
the  cream  than  by  any  other  constituent.  The  less  fat 
there  is  in  normal  cream,  the  more  casein  there  will  be, 
and  the  greater  the  per  cent,  of  acidity  needed.  The 
more  fat  there  is  in  cream,  the  less  calcium  casein  there 
will  be,  and  the  less  the  amount  of  acid  needed.  These 
statements  conform  to  practical  experience.  Thus, 
it  is  found  that  in  cream  containing  25  per  cent,  of 
fat,  it  is  necessary  to  produce  nearly  .7  per  cent,  of 
acid  in  order  to  get  the  results  sought  by  ripening, 
while,  in  cream  containing  35  per  cent,  of  fat,  less 
than  .6  per  cent,  of  acid  is  sufficient. 

To  ascertain  how  much  acid  should  be  formed  in 


I5O  MODERN    METHODS   OF  TESTING   MILK 

cream  before  churning,  the  following  rule  is  suggested 
by  Van  Norman  (Bulletin  104,  Purdue  Univ.  Agr. 
Exp.  Sta.)  :  From  100  subtract  the  per  cent,  of  fat 
in  the  cream  tested  and  multiply  the  result  by  .9,  or, 
expressed  as  a  formula,  (100  —  per  cent,  of  fat  in 
cream) x.g.  For  example: 

Cream  with  20  per  cent,  fat  requires  .72  per  cent,  of 
acidity. 

Cream  with  25  per  cent,  fat  requires  .67  per  cent,  of 
acidity. 

Cream  with  30  per  cent,  fat  requires  .63  per  cent,  of 
acidity. 

Cream  with  35  per  cent,  fat  requires  .58  per  cent,  of 
acidity. 

The  use  of  .9  as  a  factor  for  multiplying  may  not 
suit  all  conditions  and  some  other  factor,  .8  for  exam- 
ple, may  be  used.  Each  operator  may  experiment  and 
easily  find  what  per  cent,  of  acidity  is  best  adapted  to 
the  production  of  the  butter  suiting  his  market,  and 
then  a  table  like  the  above  can  be  made,  using  .9  or 
some  other  factor. 

OUTLINE  STATEMENT  OF  SOME  SPECIAL 
PRECAUTIONS  IN  TESTING  ACIDITY 

1.  The  material  to  be  tested   for  acidity  must  be 
thoroughly  mixed  before  sampling  for  a  test. 

2.  The  water  used  in  preparing  the  alkali  solution 
and  in  rinsing  the  pipette  should  be  neither  acid  nor 
alkaline  and  should  be  soft  and  clean.     Use  distilled 
water  if  possible.    The  standard  solution  must  be  of 
the  exact  strength  desired. 


METHODS  OF  TESTING  THE  ACIDITY  OF  MILK      151 

3.  The  alkali  solution,  in  whatever  form  used,  must 
be  kept  from  contact  with  the  air  as  much  as  possible 
to  prevent  changing  strength. 

4.  When  alkaline  tablets  are  used,  prepare  a  fresh 
solution  in  order  to  be  sure  of  its  strength,  if  there  is 
any  reason  for  uncertainty. 

5.  The  alkaline  tablets  should  be  kept  dry  in  well- 
stoppered  bottles. 

6.  The  tests  should  be  made  in  a  good  light  so  that 
one  can  easily  see  the  appearance  of  the  longer-lasting 
pink  color  at  the  end  of  the  reaction. 

7.  The  appearance  of  the  pink  color  at  the  end  of 
the  test  can  usually  be  more  sharply  seen  by  diluting 
the  material  examined  with  three  or  four  times  its  vol- 
ume of  distilled  water. 


CHAPTER   XI 

Methods  of  Testing  the  Sanitary  Condition  oi 

Milk 

In  addition  to  the  compounds  contained  in  normal 
milk  (see  Chapter  I.),  milk,  as  ordinarily  produced 
and  handled,  contains  other  constituents,  such  as  living 
organisms  (especially  bacteria),  enzyms,  and  often 
other  products  due  to  abnormal  physiological  processes 
in  the  udder.  These  constituents  affect  the  value  of 
milk  as  food  and  as  material  for  the  preparation  of 
dairy  products,  such  as  cream,  butter,  cheese,  etc.  The 
presence  of  micro-organisms,  chiefly  bacteria,  and  of 
enzyms  brings  about  biochemical  or  fermentation 
changes  in  the  normal  constituents  of  milk,  which 
affect  its  healthfulness  and  keeping  quality.  Undesir- 
able ferment-producing  constituents  and  products  of 
fermentation  have  their  origin  in  dirt  and  disease.  It 
is  important,  therefore,  to  be  able,  as  far  as  possible, 
to  detect  the  presence  of  such  undesirable  constituents 
in  milk.  The  method  chiefly  relied  upon  for  determin- 
ing the  condition  of  milk  in  relation  to  biochemical 
factors  has  been  by  means  of  thorough  bacteriological 
examination,  which  is  practicable  only  in  the  hands 
of  a  specialist  furnished  with  adequate  equipment. 
There  are,  however,  other  methods  for  ascertaining 
the  sanitary  condition  of  milk  which  are  available  in 
the  hands  of  any  careful  worker  and  which  afford 
most  helpful  suggestions  in  regard  to  the  value  of 

152 


TESTING  THE  SANITARY  CONDITIONS  OF  MILK      153 

milk  in  relation  to  its  use  either  as  food  or  as  material 
for  the  manufacture  of  dairy  products ;  and  some  of 
these  methods  have  not  yet  been  utilized  as  fully  as 
they  ought  to  be. 

The  methods  of  testing  milk  in  relation  to  its  bio- 
chemical or  sanitary  condition  will  be  considered  under 
the  following  headings:  (i)  Acidity,  (2)  fermenta- 
tion tests,  (3)  enzyms,  (4)  heated  milk,  (5)  dirt  in 
suspension. 

RELATION  OF  ACIDITY  TO   SANITARY  CONDI- 
TION OF  MILK 

The  details  of  the  quantitative  methods  of  deter- 
mining acidity  in  milk  by  titration  with  standardized 
alkali  solution  have  been  given  already  (pp.  131-148), 
For  exact  results,  one  of  the  methods  given  should 
be  used.  There  are,  however,  some  very  simple  tests 
which  can  be  used  for  rough  or  preliminary  work 
under  conditions  that  do  not  permit  exact  work.  Three 
of  these  tests  we  will  describe,  (i)  the  boiling  test, 
(2)  the  alcohol  test,  and  (3)  the  alizarol  test. 

Boiling  test  for  acidity  in  milk. — A  small  amount 
of  milk  (10  to  20  cc.)  is  placed  in  a  test-tube  or  beaker 
and  brought  to  boiling.  If  it  coagulates,  the  presence 
of  more  than  0.26  per  cent,  of  acid  is  indicated,  since 
normal  milk  coagulates  on  boiling  when  it  contains 
about  0.26  per  cent,  of  lactic  acid. 

Alcohol  test  for  acidity  in  milk. — Equal  parts  (5  to 
10  cc.)  of  milk  and  alcohol  (specific  gravity,  0.89)  are 
mixed  in  a  test-tube,  and  shaken  vigorously.  Fresh, 
normal  milk  shows  no  change,  while  old  milk  and  milk 
from  diseased  udders  show  more  or  less  coagulation 


154  MODERN   METHODS  OF  TESTING   MILK 

in  flakes  of  casein,  the  size  of  the  flakes  depending  on 
the  acidity.  There  is  no  close  relation  between  this 
test  and  real  acidity  of  milk,  though  commonly  milk 
containing  more  than  0.21  per  cent,  of  acid  gives  a 
marked  precipitation  with  alcohol. 

Alizarol  test  for  acidity. — This  is  a  modification  of 
the  alcohol  test  but  is  more  useful.  The  solution  used 
is  prepared  by  adding  to  the  alcohol  small  amounts 
of  alizarine  (di-oxy-anthraquinone),  the  mixture  being 
shaken  repeatedly  until  a  perfectly  clear  solution  of 
dark  reddish-brown  color  is  formed.  The  solution  is 
of  right  strength  when  2  cc.,  added  to  an  equal 
amount  of  fresh  normal  milk,  gives  an  intense  reddish 
color,  similar  to  lilac  or  red-clover  blossoms.  This 
solution  is  very  sensitive  to  acids,  the  color  depend- 
ing on  the  degree  of  acidity,  as  shown  by  the  follow- 
ing statement  of  Morres :  With  fresh,  normal  milk 
having  0.16  per  cent,  of  acidity,  the  color  is  lilac-red; 
with  o.i 8,  pale-red;  with  0.20,  brownish-red;  with 
0.22,  reddish-brown;  with  0.25,  brown;  with  0.27, 
yellowish-brown;  with  0.31,  brownish-yellow;  with 
0.36  or  over,  yellow. 

The  degree  of  acidity  is,  to  some  extent,  an  indica- 
tion of  the  age  of  milk,  the  temperature  at  which  it 
has  been  kept,  the  condition  of  care  exercised  in  keep- 
ing it  clean,  and  of  the  abundance  of  lactic  acid 
bacteria. 

The  acidity  of  market  milk  should  usually  be  under 
0.15  per  cent,  when  it  reaches  the  consumer,  and 
should  not  exceed  0.2.  The  same  may  be  said  of 
milk  that  is  intended  for  the  purpose  of  cheese- 
making. 


TESTING  THE  SANITARY  CONDITIONS  OF  MILK     155 

FERMENTATION  TESTS  IN  RELATION  TO  SANI- 
TARY  CONDITION   OF   MILK 

Milk  frequently  contains  objectionable  forms  of 
organisms  or  ferments  that  are  not  made  perceptible 
by  ordinary  methods  of  observation.  The  condition 
arises  particularly  in  milk  used  for  cheese-making  and 
may  result  in  serious  injury  to  the  quality  of  the 
cheese.  Several  different  forms  of  taste  have  been  pro- 
posed which  will  enable  one  to  detect  the  presence  of 
certain  types  of  organisms  through  the  results  of  their 
biochemical  action.  Of  the  different  forms  we  will 
describe  two,  (i)  the  Wisconsin  test  and  (2)  that  of 
Gerber. 

Wisconsin  fermentation  or  curd  test. — The  Wis- 
consin Experiment  Station  (Wis.  Exp.  Sta.  I2th  and 
I5th  Annual  Reports,  1895  and  1898)  has  applied  cer- 
tain principles  to  the  development  of  a  test  that  enables 
one  to  identify  milk  containing  certain  forms  of  unde- 
sirable ferments  likely  to  do  serious  injury.  This  meth- 
od is  based,  in  general,  upon  the  plan  of  making  con- 
ditions favorable  for  the  rapid  development  of  the  fer- 
ments present  in  milk. 

Apparatus. — The  apparatus  consists  of  the  follow- 
ing parts:  (i)  Pint  glass  jars  or  tin  cans  with  covers; 
(2)  a  well  insulated  tank  to  hold  the  jars,  (3)  rennet 
extract,  (4)  a  thermometer,  (5)  a  case-knife  or  simi- 
lar instrument  for  cutting  curd,  and  (6)  a  small  pipette 
for  measuring  rennet-extract. 

Operation  of  test. — The  test  is  conducted  as  fol- 
lows: The  jars,  including  covers,  just  previous  to 
use,  are  sterilized  with  live  steam,  scalding  water  or 
dry  heat  (212°  F.).  Each  jar  or  can  is  filled  about 


156  MODERN   METHODS  OF  TESTING   MILK 

two-thirds  full  with  the  milk  to  be  tested  and  the  ster- 
ilized cover  put  on  at  once.  The  jars  are  then  placed 
in  the  tank  which  is  filled  with  water  at  100°  to  102° 
F.  up  to  the  upper  surface  of  the  milk  in  the  jars.  The 
temperature  of  the  water  should  be  kept  at  100°  to 
102°  F.  during  the  whole  operation.  To  hasten  the 
warming  of  the  milk,  the  jars  are  taken  out  and  shaken 
occasionally.  The  temperature  of  the  milk  is  observed 
with  a  sterile  thermometer,  and  when  the  milk  has 
reached  98°  F.,  one  adds  10  drops  of  rennet-extract 
to  each  jar  and  mixes  thoroughly  by  giving  the  con- 
tents of  the  jar  a  rotary  motion.  When  the  milk  has 
coagulated,  it  is  allowed  to  stand  until  it  is  firm,  usu- 
ally about  20  minutes.  To  enable  the  whey  to  sepa- 
rate more  readily,  the  curd  is  then  cut  fine  with  a 
thin  knife,  which  must  be  carefully  rinsed  with  hot 
water  after  finishing  each  jar  and  before  using  it  in 
another,  in  order  to  avoid  carrying  contamination  from 
one  milk  to  another  and  spoiling  the  test.  The  curd 
is  allowed  to  settle  completely.  When  the  whey  has 
been  separating  half  an  hour,  the  samples  are  exam- 
ined for  flavor  by  smelling,  after  which  the  whey 
is  carefully  poured  out  of  the  jars  and  this  is  re- 
peated at  intervals  of  30  to  40  minutes  for  8  hours 
or  more.  Under  the  favorable  conditions  of  tempera- 
ture, similar  to  those  employed  in  cheese-making,  the 
organisms  present  develop  readily  and  reveal  their 
presence  in  different  characteristic  ways.  The  jars 
are  finally  opened,  any  whey  present  is  drained  off, 
and  the  following  tests  are  applied:  (i)  The  curd  is 
cut  into  two  pieces.  The  curd  will  be  solid  and  free 
from  holes  on  the  cut  surfaces,  if  the  milk  is  not 


TESTING  THE   SANITARY  CONDITIONS   OF  MILK      157 

tainted.  If  it  is  spongy  and  full  of  holes,  it  con- 
tains those  undesirable  organisms  that  produce  gases 
in  the  curd  and  injure  it  for  cheese-making,  showing 
in  the  form  of  "floating  curds"  and  "huffy"  cheese. 
The  holes  are  usually  small,  their  common  name  be- 
ing "pin-holes."  (2)  The  curd  is  examined  with  ref- 
erence to  any  marked  disagreeable  odors  that  may 
be  present.  Some  undesirable  organisms  reveal  their 
presence  by  smell  without  making  spongy  curd.  This 
may,  perhaps,  be  best  perceived  by  smelling  of  a 
freshly  cut  surface  of  the  curd.  Offensive  odors  are, 
of  course,  an  undesirable  indication.  Special  appara- 
tus for  performing  the  test  is  furnished  by  dairy-sup- 
ply houses,  but  pint  fruit- jars  and  other  home-made 
appliances  will  answer  satisfactorily. 

By  this  method  one  can  learn  what  particular  lot 
of  milk  among  several  is  responsible  for  undesirable 
fermentations.  Moreover,  having  traced  the  source  of 
contamination  to  a  single  herd  of  cows,  it  is  easily 
possible,  applying  the  test  to  single  cows,  to  ascer- 
tain which  individual  or  individuals  may  be  the  source 
of  trouble. 

Precautions. — Two  points  must  be  carefully  ob- 
served in  carrying  out  this  test :  ( i )  The  temperature 
must  be  kept  as  near  98°  F.  as  possible,  in  order  that 
the  bacteria  may  develop  as  desired.  This  can  be 
done  by  keeping  the  temperature  of  the  water  sur- 
rounding the  jars  at  100°  to  102°  F.  The  tempera- 
ture must  be  watched.  (2)  The  thermometer  and  the 
knife  used  should  be  made  not  only  clean  but  sterile 
each  time  after  using  in  one  sample  before  placing 
them  in  another. 


158  MODERN    METHODS  OF  TESTING   MILK 

Gerber's  fermentation  test. — This  test  consists  in 
heating  milk  in  tubes  6  hours  at  104°  to  106°  F.  and 
then  observing  the  odor,  appearance,  taste,  etc.,  for 
abnormal  qualities.  The  milk  is  heated  a  second  time 
for  6  hours  at  104°  to  106°  F.  Any  abnormal  coagula- 
tion of  the  milk  is  noticed,  such  as  holes  due  to  gas. 
Gerber  states  that  milk  coagulating  in  less  than  12 
hours  is  abnormal,  due  either  to  the  abnormal  char- 
acter of  the  milk  itself  when  drawn  or  to  improper 
care  after  being  drawn.  Milk  that  does  not  curdle 
within  24  to  48  hours  is  open  to  the  suspicion  of  con- 
taining preservatives  and  should  be  examined  for  such 
substances. 

METHODS  OF  TESTING  FOR  ENZYMS  IN  MILK 

Enzyms  are  chemical  ferments;  they  have  the 
power  to  produce  changes  in  other  substances  without 
themselves  undergoing  appreciable  change.  Enzyms 
are  the  products  of  living  cells ;  those  in  milk  have  their 
origin,  in  part,  in  the  animal  producing  the  milk  and 
usually,  in  larger  part,  in  the  bacteria  contained  in 
the  milk.  Under  this  head  we  shall  consider  the  fol- 
lowing tests:  (i)  Reductase,  (2)  catalase,  (3)  dis- 
tinction between  heated  and  unheated  milk. 

Reductase  test. — Ordinary  normal  milk  possesses 
the  power  of  decolorizing  certain  coloring-substances 
by  reduction  or  removal  of  oxygen ;  this  property  ap- 
pears to  depend  upon  the  presence  of  micro-organisms 
in  milk  since  the  larger  the  number  of  bacteria,  the 
shorter  the  time  required  to  produce  decolorization. 
The  coloring-substance  that  has  been  found  especially 
useful  in  this  test  is  a  compound  known  as  methylene- 


TESTING  THE  SANITARY  CONDITIONS   OF  MILK      159 

blue;  this  does  not  combine  with  casein  and  is  easily 
absorbed  by  living  cells.  A  solution  of  this  is  pre- 
pared by  putting  a  few  grams  of  a  solution  of  methyl- 
ene-blue  (using  the  zinc  chloride  double  salt)  into 
20  cc.  of  alcohol  and  letting  it  stand  at  room  tempera- 
ture for  2  hours.  Of  this  saturated  solution  take  5  cc. 
and  mix  it  with  195  cc.  of  distilled  water. 

To  perform  the  Barthel  form  of  the  test,  add  I  cc.  of 
the  dilute  methylene-blue  solution  to  20  cc.  of  milk  and 
put  the  mixture  in  a  warm  place  (113°  to  122°  F.). 
If  the  blue  color  disappears  within  an  hour,  the  milk  is 
to  be  regarded  as  very  bad  from  a  sanitary  point  of 
view  and  wholly  unfit  for  the  use  of  infants.  If  the 
color  disappears  within  3  hours,  the  milk  is  classed  as 
of  second  quality ;  milk  which  remains  wholly  un- 
changed after  the  lapse  of  3  hours  is  to  be  regarded  as 
good. 

Another  simple  way  of  performing  the  test  is  to 
mix  25  cc.  of  milk  and  6  drops  of  a  solution  of  pure 
methylene-blue  ( 1 14000)  in  a  cylinder.  After  shaking, 
the  cylinder  is  stoppered  with  a  cotton  plug  and  put  in 
a  water-bath  at  104°  F.  If  the  color  disappears  in  less 
than  15  minutes,  the  milk  is  condemned. 

This  test  is  used  as  a  rough  measure  of  the  num- 
ber of  bacteria  in  milk,  since  the  decoloration  or  reduc- 
tion of  methylene-blue  in  milk  appears  to  be  due  whol- 
ly to  the  activity  of  micro-organisms.  The  decolor- 
ation takes  place  in  5  minutes  or  less  when  the  number 
of  bacteria  exceeds  10  millions  per  cubic  centimeter. 

Jensen's  "reduction-fermentation"  test  is  a  modifica- 
tion of  the  Barthel  method,  using  only  0.5  cc.  of  methyl- 
ene-blue solution  (instead  of  i  cc.)  and  heating  at 


l6o  MODERN    METHODS   OF  TESTING   MILK 

100°  to  104°  F.  This  method  is  more  sensitive,  de- 
colorization  taking  place  more  quickly.  Milk  in 
which  the  blue  color  disappears  in  15  minutes  is  re- 
garded as  unfit  for  use.  The  samples  of  milk  are  al- 
lowed to  remain  at  the  same  temperature  for  the 
fermentation  test  and,  at  the  end  of  24  hours,  the  con- 
ditions are  observed  as  in  connection  with  the  Wiscon- 
sin fermentation  test  (p.  155).  This  method  gives  use- 
ful evidence  in  regard  to  the  abundance  of  living 
organisms  present  as  well  as  the  kinds  of  organisms 
present. 

Catalase  test. — Normal  fresh  milk  has  the  property 
of  decomposing  hydrogen  peroxide  into  free  oxygen 
gas  and  water.  This  is  believed  to  be  due  in  part  to 
the  presence  of  white  blood  corpuscles  (leucocytes), 
which  are  always  present  in  milk,  and  in  part  to  the 
action  of  micro-organisms.  Substances  in  milk  having 
the  power  to  decompose  hydrogen  peroxide  are  known 
under  the  general  name  of  catalase.  It  increases  with 
the  age  of  milk  and  is  present  more  abundantly  in  milk 
of  diseased  cows. 

The  amount  of  catalase  in  milk  can  be  estimated 
by  treating  a  certain  amount  of  milk  with  a  certain 
amount  of  hydrogen  peroxide  under  given  conditions 
and  measuring  the  free  oxygen  that  is  given  off.  Sev- 
eral forms  of  apparatus  have  been  devised  for  the  pur- 
pose. 

The  test  is  performed  as  follows:  In  a  small  fer- 
mentation tube  or  other  suitable  apparatus,  we  mix 
15  cc.  of  milk  and  5  cc.  of  i  per  cent,  hydrogen  per- 
oxide; then  place  the  apparatus  at  a  temperature  of 
77°  to  86°  F.  The  amount  of  gas  formed  at  the  end 


TESTING  THE   SANITARY  CONDITIONS  OF  MILK      l6l 

of  2  hours  is  observed.  Milk  older  than  2  to  6  hours 
giving  4  cc.  of  oxygen  by  this  test  is  regarded  as  ab- 
normal. 

This  test  has  been  found  useful  in  detecting  ab- 
normal conditions  in  the  milk  of  individual  cows.  A 
high  catalase  content  in  fresh  normal  milk  is  a  sign 
of  diseased  udder  after  the  colostral  period  is  over. 
Increase  of  catalase  in  milk  several  (6  to  12)  hours 
old  indicates  bacterial  activity  and  may  be  used  as  a 
test  of  the  keeping  power  of  milk. 

Methods  for  testing  heated  milk. — It  is  often  desir- 
able to  know  whether  milk  has  been  heated  or  not. 
In  the  case  of  pasteurized  milk,  it  is  important  to  learn 
whether  it  has  been  heated  sufficiently  to  be  really 
pasteurized. 

Several  tests  have  been  devised  for  distinguishing 
between  heated  and  unheated  milk.  They  are  based 
on  the  following  facts:  Unheated  milk  contains 
enzyms  which,  in  the  presence  of  peroxides,  such  as  hy- 
drogen peroxide,  set  free  oxygen  and  this  oxygen 
produces  marked  coloration  when  certain  compounds 
are  present.  These  enzyms,  when  subjected  to  a  tem- 
perature above  172°  to  176°  R,  are  so  changed  that 
they  lose  the  power  of  setting  free  oxygen  from  a 
peroxide  and  therefore  they  produce  little  or  no  color 
in  milk  so  heated.  Several  different  substances  have 
been  used,  giving  rise  to  as  many  tests,  of  which  we 
will  describe  the  following:  (i)  Para-phenylene-dia- 
mine  test,  (2)  Guaiac  test,  (3)  Methylene-blue  test. 

Para-phenylene-diamine  or  Storch  test. — Into  a  cup 
or  test-tube  one  puts  about  5  cc.  of  milk,  then  one  drop 
of  a  0.2  per  cent,  solution  of  hydrogen  peroxide  and 


l62  MODERN   METHODS  OF  TESTING  MILK 

two  drops  of  a  2  per  cent,  solution  of  para-phenylene- 
diamine  hydrochloride.  The  mixture  -is  well  shaken. 
If  the  milk  has  not  been  heated  at  all  or  to  a  tempera- 
ture not  above  172°  F.,  an  intensely  blue  color  appears. 
If,  however,  after  half  a  minute  a  clear,  grayish-blue 
color  appears,  the  milk  has  been  heated  up  to  175°  F.  or 
higher.  The  reaction  is  of  sufficient  delicacy  to  detect 
10  per  cent,  of  milk  heated  below  172°  F.  in  a  lot  of 
milk  pasteurized  above  this  temperature. 

The  solution  of  para-phenylene-diamine  hydrochlor- 
ide does  not  keep  longer  than  2  months  and  a  new  pre- 
paration .should  be  made. 

The  test  can  be  applied  to  cream  or  to  butter.  Melt 
about  10  grams  of  butter  in  a  cup  or  beaker,  heating 
to  105°  to  115°  F.,  add  10  cc.  of  warm  water,  2  drops 
of  0.3  per  cent,  hydrogen  peroxide  solution  and  sev- 
eral drops  of  para-phenylene-diamine  solution.  Pour 
the  mixture  into  a  cream-testing  bottle,  shake  vigorous- 
ly and  whirl  in  centrifuge  I  minute.  In  the  watery 
solution  that  separates  from  the  fat,  a  blue  color  ap- 
pears if  the  cream  from  which  the  butter  was  made 
was  not  pasteurized. 

Guaiac  or  Arnold  test  for  heated  mik. — To  a  small 
amount  of  milk  in  a  cup  or  test-tube  are  added  5  or 
10  drops  of  guaiac  tincture  (preferably  a  5  or  10  per 
cent,  solution  prepared  by  dissolving  guaiac  resin  in 
acetone)  and  the  mixture  shaken.  In  case  of  milk 
heated  to  less  than  176°  F.,  a  blue  color  appears  after 
some  minutes ;  if  it  has  been  heated  above  176°  F., 
no  coloration  appears.  The  precaution  should  always 
be  taken  to  test  the  guaiac  solution  with  unheated  milk, 
because  some  solutions  produce  no  coloration  even  in 


TESTING   THE   SANITARY  CONDITIONS   OF  MILK      163 

such  milk.  This  can  be  remedied  by  adding  a  few 
drops  of  hydrogen  peroxide  to  the  solution. 

A  modification  of  this  test  can  be  used :  To  I  cc.  of 
milk,  one  adds  I  cc.  of  a  water  solution  of  guaiacol 
and  i  drop  of  hydrogen  peroxide  solution  (3  per  cent.). 
In  unheated  milk  a  strong  orange  color  appears,  but 
not  in  case  of  milk  previously  heated  to  176°  F. 

Methylene-blue  or  Schardinger's  test. — The  re- 
agent used  in  this  test  is  a  mixture  of  5  cc.  of  a  satu- 
rated solution  of  methylene-blue,  5  cc.  of  formalin  and 
190  cc.  of  distilled  water.  The  test  is  performed  as 
follows :  To  20  cc.  of  milk  add  i  cc.  of  Schardinger's 
reagent,  warm  to  113°  to  122°  F.  and  observe  the  time 
it  requires  to  lose  the  color  completely.  Ordinary 
normal  milk  is  decolorized  in  about  10  minutes  with 
this  test. 

The  reaction  depends  upon  a  specific  enzym  in  milk 
called  aldehyde-reductase,  which  is  more  or  less  quick- 
ly destroyed  at  temperatures  above  158°  F.,  while  with 
milk  heated  above  176°  F.  decolorization  is  complete. 
When  milk  is  pasteurized  either  2  minutes  at  167°  F. 
or  about  15  minutes  at  158°  F.  the  color  disappears  in 
about  30  minutes  with  the  test. 

METHODS  OF  TESTING  MILK  FOR  SUSPENDED 

DIRT 

In  making  an  examination  of  milk  with  reference 
to  its  sanitary  condition,  dirt  in  suspension  or  sedi- 
ment should  always  be  tested  for.  There  are  several 
satisfactory  methods.  It  is  sufficient  for  most  pur- 
poses to  get  a  rough  idea  of  the  amount  of  sediment. 
There  are  three  general  methods  in  use :  ( i )  By  filtra- 


164  MODERN    METHODS   OF  TESTING   MILK 

tion,  (2)  by  centrifugal  machine,  (3)  by  ordinary  set- 
tling. 

Filtration  test  for  dirt. — This  can  be  carried  out 
in  a  very  simple  form  by  packing  a  funnel  with  some 
absorbent  cotton  and  pouring  a  pint  of  milk  on  this. 
Most  of  the  dirt  will  collect  on  the  top  of  the  cotton 
if  it  is  not  packed  too  loose. 

The  Wisconsin  experiment  station  (Bulletin  195) 
has  made  a  special  device  (Lorenz  sediment-tester) 
for  the  application  of  this  principle,  which  furnishes 
a  convenient  and  effective  means  for  filtering  or  strain- 
ing dirt  from  milk.  The  details  of  construction  are 
shown  in  Fig.  40.  In  operating  the  test,  a  cotton 
disc  is  placed  in  the  cap  over  the  wire  gauze  and  then 
fastened  in  place.  A  pint  of  milk  is  .then  poured  into 
the  cylinder  or  funnel  (A).  When  the  milk  has  run 
through  the  filter,  the  cotton  disc  is  removed  and 
placed  on  a  piece  of  white,  clean  paper  to  dry.  Then 
another  disk  can  be  inserted  and  another  sample  of 
milk  tested  and  the  operation  repeated  for  any  desired 
number  of  samples.  When  many  samples  are  tested 
in  rapid  succession,  a  numbered  cap  should  be  pro- 
vided for  each  test. 

The  rapidity  of  testing  many  lots  of  milk  depends 
on  (i)  the  temperature  of  the  milk  while  filtering 
and  (2)  on  the  character  of  the  cotton  filtering-discs. 
The  milk  filters  more  rapidly  if  it  is  kept  hot;  the 
apparatus  provides  for  this  condition.  The  cotton 
discs  should  be  made  of  absorbent  cotton  that  is  en- 
tirely free  from  starch  or  similar  material.  The  discs 
should  be  about  one-eighth  inch  thick  and  cut  out 
to  fit  the  cap  and  wire  gauze.  When  properly  made, 


FIG    40 — DETAILS    OF    CONSTRUCTION     OF    WISCONSIN    OR    LORE1T2 
DIRT  TESTER 


The  central  cylinder  A,  through  which  the  milk  is  poured  is  2J£  inch«« 
in  diameter  and  6  inches  long,  surrounded  by  a  steam  or  hot  water 
jacket  and  with  a  half-inch  intervening  space.  The  steam  or  hot  water 
enters  at  the  lower  opening  and  overflows  at  B.  The  brass  cap  C  slips 
over  the  bottom  of  the  inner  cylinder  and  is  held  in  place  by  a  clamp 
rod  D.  This  cap  contains  a  circle  of  wire  gauze  E,  over  which  is  placed 
the  disc  of  absorbent  cotton.  The  cap  may  be  quickly  removed  by 
swinging  the  clamp  rod  D  to  one  side  and  the  dirty  filter  tnay  be 
replaced  by  a  clean  one. 


i66 


MODERN    METHODS  OF  TESTING   MILK 


they  allow  the  hot  milk  to 
filter  rapidly  but  retain  the 
dirt  suspended  in  the  milk. 
Centrifugal  test  for  dirt. 
— A  small  centrifugal  ma- 
chine that  is  made  to  run  at 
a  higher  speed  than  the  Bab- 
cock  testers  is  used.  A  form 
of  hand-centrifuge  is  shown 
in  Fig.  41.  Special  gradu- 
ated tubes  (Fig.  42)  are 
made  to  use  in  this.  The 
milk  to  be  tested  is  stirred 
thoroughly,  the  tube  is  filled 
to  the  highest  mark,  placed 
in  the  pocket  of  the  centri- 
fuge and  whirled  several 
minutes.  The  sediment  col- 


FIG.    41 — HAND-CENTRIFUGE 
FOR    SEDIMENTATION    WORK 


FIG.  42— TUBE  FOR 
SEDIMENTATION  WORK 


FIG.  43 — BAUSCH  &  LOME 

ELECTRIC  CENTRIFUGE 
Speed,   1,000  revolutions  per  minute 


fc 

w 

I 
I 

8 


B 

8 


1 


167 


l68  MODERN    METHODS   OF   TESTING    MILK 

lects  at  the  bottom  and  can  be  easily  measured  by 
reading  the  amount  on  the  scale.  In  Fig.  43  is  shown 
a  Bausch  and  Lomb  electric  centrifuge.  This  com- 
pany also  furnishes  hand-centri- 
fuges capable  of  3,000  to  8,000 
revolutions  per  minute.  Their 
centrifuges  and  tubes  can  be 
used  also  in  testing  for  fat  in 
milk  by  the  Babcock  method. 
In  Fig.  44  is  shown  another  FIG 

form     of     electrical     centrifuge   GLASS  FOR  COLLECTING 

t  .    i        .  ,•    £  e  SEDIMENT  IN   MILK 

which    is   very    satisfactory    for 
collecting  sediments. 

Settling  test  for  dirt. — A  method  less  accurate,  but 
fairly  satisfactory  in  the  absence  of  any  better  means, 
is  to  place  about  4  ounces  of  milk  in  a  test-glass  (Fig. 
45)  and  let  it  stand  for  one  or  two  hours.  The  dirt 
collects  in  the  bottom  and  its  amount  can  be  roughly 
estimated  by  the  eye. 


CHAPTER  XII 

Methods  of  Testing  Milk  by  Rennet-Extract 
and  Pepsin 

In  cheese-making  it  is  necessary  to  have  some  means 
of  finding  out  when  the  rennet-extract  should  be  ad- 
ded to  milk  in  order  to  secure  the  best  results  in  the 
process.  This  is  usually  known  as  "testing  the  ripe- 
ness of  milk."  Two  methods  are  in  common  use  for 
this  purpose:  (i)  The  Monrad  test  and  (2)  the 
Marschall  test. 

THE  MONRAD  TEST 

This  test  is  based  upon  the  amount  of  time  re- 
quired for  a  definite  quantity  of  milk  at  a  given  tem- 


FIG.    46  —  MONRAD  RENNET-TEST 


perature  to  become  coagulated  by  a  fixed  quantity  of 
rennet. 

The  pieces  of  apparatus  (Fig.  46)  required  are  the 
following:  (i)  A  tin  cylinder  for  measuring  milk, 
holding,  when  full,  160  cc.,  (2)  a  5  cc.  pipette,  (3)  a 

169 


I7O  MODERN     METHODS    OF    TESTING     MILK 

50  cc.  glass  flask,  (4)  a  thermometer,  and  (5)  a  half- 
pint  tin  basin. 

In  testing  the  ripeness  of  milk  by  means  of  rennet- 
extract,  one  first  prepares  a  dilute  solution  of  the 
rennet,  as  follows:  One  measures  with  the  small  pi- 
pette 5  cc.  of  rennet-extract  into  the  50  cc.  flask.  The 
pipette  is  then  rinsed  twice  with  water  by  sucking  it 
full  of  cold,  clean  water  to  the  mark,  the  rinsings  also 
being  run  into  the  50  cc.  flask.  The  flask  is  then  filled 
with  water  to  the  50  cc.  mark,  and  the  contents  are 
well  mixed  by  shaking.  The  next  step  is  to  fill  the 
tin  cylinder  with  the  well-mixed  milk  to  be  tested  and 
this  is  emptied  into  the  half-pint  basin.  The  milk 
must  be  at  the  temperature  at  which  one  adds  the 
rennet  in  cheese-making,  which  is  generally  about  85° 
or  86°  F.  To  the  milk  at  the  desired  temperature,  one 
adds  5  cc.  of  the  diluted  rennet  solution,  mixes  it 
through  the  milk  quickly,  using  the  thermometer  as 
a  stirrer.  The  exact  time  when  the  rennet-extract  is 
added  to  the  milk  is  noted  by  the  second-hand  of  a 
watch  and  then  again  when  the  milk  has  coagulated; 
the  number  of  seconds  required  to  coagulate  the  milk 
is  recorded.  The  exact  point  of  coagulation  can  be 
seen  more  sharply  by  scattering  a  few  particles  of 
charcoal  (as  the  blackened  end  of  a  partly  burned 
match)  on  the  surface  of  the  milk,  and  then  with  the 
thermometer  starting  the  surface  into  motion  around 
the  dish.  The  black  particles  stop  the  instant  the 
milk  coagulates.  By  using  a  stop-watch,  great  accu- 
racy and  delicacy  can  be  attained.  Care  should  be 
taken  to  keep  the  temperature  of  the  milk  at  85°  or 
86°  F.,  testing  frequently  with  the  thermometer;  and, 


TESTING  BY  RENNET-EXTRACT  AND  PEPSIN         171 

in  case  the  temperature  drops,  it  can  be  raised  by  plac- 
ing the  basein  of  milk  in  warm  water.  In  ordinary 
cheddar  cheese-making,  milk  is  ready  for  the  addition 
of  rennet  when  it  coagulates  in  30  to  60  seconds  un- 
der the  foregoing  conditions. 


THE  MARSCHALL  TEST 

In  this  test  the  same  general  procedure  is  followed 
as  in  the  Monrad  test,  but  the  rate  of  coagulation  is 
observed  in  a  different  way.  The  following  pieces  of 
apparatus  (Fig.  46a)  are 
used:  (a)  A  testing  cup 
or  basin,  of  about  a  pint 
capacity,  for  holding  the 
milk  to  be  tested.  On  the 
inside  wall  of  this  cup  there 
are  graduated  spaces  be- 
ginning with  zero  at  the 
top  and  going  by  half-divis- 
ions to  7  near  the  bottom 
of  the  cup,  while  in  the  bot- 
tom of  the  cup  is  a  metal 
tube  with  a  very  small  bore, 
(b)  An  ounce  bottle  with  a  mark  on  it  to  indicate  20 
cc.  (c)  A  spatula  for  stirring  the  milk,  (d)  A  I  cc. 
pipette. 

The  operation  of  conducting  this  test  is  as  follows : 
Measure  with  the  pipette  i  cc.  of  the  rennet-extract 
used  and  empty  it  into  the  ounce  bottle,  previously 
half  filled  with  clean  cold  water.  Rinse  the  pipette 
two  or  three  times  by  drawing  water  into  it  from  the 


FIG.  460 
MARSCHALL  RENNET-TEST 


172  MODERN   METHODS  OF  TESTING   MILK 

bottle  and  allowing  it  to  run  back  into  the  bottle.  Mix 
well  by  shaking.  Then  place  the  milk  to  be  tested 
in  the  test-cup,  setting  it  in  a  level  position  and  allow- 
ing the  milk  to  run  out  at  the  bottom.  Taking  the  bot- 
tle of  diluted  rennet  in  one  hand  and  the  spatula  in 
the  other,  watch  the  level  of  the  milk  in  the  cup.  The 
moment  the  upper  surface  of  the  milk  drops  to  the 
zero  mark,,;  pour  the  diluted  rennet  into  the  milk  and 
stir  well.  Then  leave  it  alone.  When  the  milk  coagu- 
lates, it  stops  running  through  the  metal  tube.  From 
the  graduated  scale,  read  the  number  of  spaces  un- 
covered on  the  inside  of  the  cup,  showing  how  many 
divisions  of  milk  have  run  out.  The  more  slowly  the 
milk  coagulates,  the  larger  the  amount  that  runs  out; 
the  more  quickly  the  milk  coagulates,  the  smaller  the 
amount  that  runs  out  and  the  fewer  spaces  there  are 
uncovered.  When  about  2^2  spaces  are  uncovered, 
the  milk  is  ready  for  addition  of  rennet.  The  tempera- 
ture must  be  watched,  being  tested  at  the  start  and 
finish,  especially  in  a  cold  room. 

In  the  Marschall  test,  as  originally  devised,  there 
were  some  objectionable  features.  Formerly,  glass 
tubing  was  used  in  the  bottom  of  the  cup  and  it  was 
found  that  the  size  of  the  bore  of  tubing  unavoidably 
varied  in  different  cups.  This  made  it  impossible  to 
compare  the  results  of  one  cup  with  those  of  another, 
unless  they  were  proved  by  actual  testing  to  be  alike. 
This  difficulty  has  been  overcome  by  dispensing  with 
the  use  of  glass  tubing  and  substituting  in  its  place 
aluminum  tubing  with  the  hole  drilled  to  uniform  ex- 
actness. One  difficulty  connected  with  the  use  of  the 
Marschall  test  is  that  a  little  speck  of  dirt  quickly 


TESTING  BY  RENNET-EXTRACT  AND  PEPSIN         173 

clogs  the  tube  and,  therefore,  special  pains  must  be 
taken  to  keep  it  open.  For  ordinary  work  the  Mar- 
schall  test  is  convenient  but  it  is  not  capable  of  as 
great  delicacy  as  is  the  Monrad  test. 

METHOD    OF   TESTING   RENNET-EXTRACTS 

Rennet-extract  is  prepared:  by  soaking  calves'  stom- 
achs in  dilute  brine.  This  treatment  dissolves  from 
the  mucous  membrane  the  enzym  or  chemical  ferment 
that  has  the  property  of  coagulating  milk-casein,  a 
property  upon  which  the  process  of  cheese-making  is 
dependent.  The  ferment  contained  in  rennet-extracts 
appears  to  be  the  same  as  pepsin  in  regard  to  its  ac- 
tion upon  milk  casein.  Different  brands  of  rennet-ex- 
tract vary  somewhat  in  their  strength,  that  is,  the 
rapidity  and  completeness  with  which  they  coagulate 
milk  when  used  in  the  same  amount.  It  is,  therefore, 
important  to  have  a  means  of  testing  their  strength, 
in  order  that  their  value  may  be  definitely  known  and 
that  cheese-makers  may  be  able  to  know  in  advance 
of  using  how  much  they  must  use  for  the  best  results. 
The  Monrad  and  Marschall  tests  are  available  for 
this  purpose. 

In  order  to  test  the  comparative  strength  of  differ- 
ent rennet-extracts,  one  treats  different  portions  of 
the  same  milk  with  the  different  extracts  to  be  tested. 
In  all  other  respects,  the  details  of  the  methods  pre- 
viously given  are  followed.  All  conditions  must  be 
kept  alike  in  the  different  tests.  The  strength  of  the 
rennet-extracts  is  shown  by  the  rapidity  with  which 
the  milk  is  coagulated;  the  stronger  the  rennet,  the 
less  the  time  of  coagulation. 


174  MODERN    METHODS  OF  TESTING   MILK 

METHOD   OF  TESTING  PEPSIN 

Pepsin  is  beginning  to  be  used  in  cheese-making  as 
a  substitute  for  rennet-extract.  Vivian  has  worked 
out  the  important  details.  The  scale-pepsin,  of  strength 
known  as  1-3,000,  prepared  from  stomachs  of  sheep, 
is  recommended.  It  may  be  used  at  the  rate  of  5 
grams  for  1,000  pounds  of  milk.  In  testing  scale- 
pepsin  by  the  rennet  test,  one  can  dissolve  the  scale- 
pepsin  at  the  rate  of  5  grams  in  4  ounces  of  water  and 
use  this  solution  exactly  like  a  rennet-extract  with 
milk.  It  should  be  tested  in  comparison  with  a  sam- 
ple of  rennet-extract  whose  use  in  cheese-making  has 
been  tested,  the  test  being  made  on  different  portions 
of  the  same  milk. 

TESTING  THE  AGE  OF  MILK  BY  RENNET-TEST 

The  age  of  milks  and  the  care  with  which  they  have 
been  kept  can  also  be  tested  in  a  comparative  way  by 
the  rennet-test,  since  with  the  same  rennet-extract  or 
pepsin  solution  different  milks  generally  coagulate 
more  rapidly  in  proportion  to  the  amount  of  acid  con- 
tained in  them,  especially  if  the  amount  of  lactic  acid 
is  considerable. 


CHAPTER  XIII 

Methods  of  Testing  Specific  Gravity  and  Solids 
of  Milk  by  the  Lactometer 

The  specific  gravity  of  milk  may  furnish  important 
information,  which  becomes  of  special  value  when 
taken  in  connection  with  the  amount  of  fat  present. 
Thus,  with  the  data  furnished  by  the  specific  gravity 
and  the  per  cent,  of  fat,  we  can  easily  calculate  the 
amount  of  solids  in  milk  and  the  amount  of  solids- 
not-fat. 

THE  SPECIFIC  GRAVITY  OF  MILK 

Definition  of  specific  gravity. — By  the  specific  grav- 
ity of  milk,  we  mean  the  weight  of  a  given  bulk  or 
volume  of  milk  as  compared  with  the  weight  of  an 
equal  volume  of  water  at  the  same  temperature.  To 
illustrate,  suppose  we  have  a  vat  which,  when  just  full 
of  water,  contains  exactly  1,000  pounds  of  water  at 
60°  F.  Now,  if  we  fill  such  a  vat  full  of  milk  of  aver- 
age composition  at  the  same  temperature,  this  amount 
of  milk  weighs  1,032  pounds.  This  is  so  because  the 
milk  contains,  in  addition  to  the  water  in  it,  several 
solid  substances  heavier  than  water.  In  this  illustra- 
tion we  express  the  relation  or  ratio  of  the  equal  vol- 
umes of  water  and  milk  by  dividing  1,032  by  1,000; 
the  result,  1.032,  is  the  specific  gravity  of  the  milk. 

i75 


176  MODERN    METHODS   OF   TESTING   MILK 

Variation  in  specific  gravity  of  milk. — Since  the 
specific  gravity  of  milk  largely  depends  upon  the 
amount  of  solids  in  it  heavier  than  water,  the  specific 
gravity  should  vary,  since  we  know  that  the  amount 
of  solids  in  milk  varies  considerably.  And  so  we  find 
the  specific  gravity  of  some  milks  below  1.030  and  of 
some  others  above  1.035  I  but  most  normal  milks  from 
herds  of  cows  have  specific  gravities  lying  between 
1.030  and  1.034. 

The  solids  of  milk  heavier  than  water  are  casein, 
albumin  and  milk-sugar.  They  constitute  the  solids- 
not-fat  of  milk  and  have  a  specific  gravity  of  about 
1.500. 

Effect  of  milk-fat  on  specific  gravity  of  milk. — 
Milk-fat  is  lighter  than  water,  its  specific  gravity  be- 
ing about  0.900  compared  with  that  of  water  as  i.ooo. 
Therefore,  an  increase  of  fat  in  milk,  relative  to  the 
other  solids,  lowers  the  specific  gravity  of  milk.  Thus, 
by  adding  cream  to  normal  milk,  we  can  r^ake  its 
specific  gravity  lower  than  that  of  normal  milk.  On 
the  other  hand,  by  removing  fat  from  milk,  we  in- 
crease the  specific  gravity,  because  we  remove  what 
is  lighter,  and  leave  what  is  heavier,  than  water. 

Effect  of  adding  water  and  other  substances  to 
milk. — Water  being  lighter  than  milk,  the  specific 
gravity  of  milk  is  lowered  by  addition  of  water.  There- 
fore, it  is  easily  possible  by  removing  cream  from  nor- 
mal milk  to  increase  the  specific  gravity  and  then,  by 
adding  water,  to  decrease  the  specific  gravity  again 
to  that  of  normal  milk.  The  addition  of  sugar,  salt  or 
any  similar  substance  to  milk  increases  the  specific 
gravity.  Since  water  has  been  the  most  common  adul- 


TESTING  BY   THE   LACTOMETER 


177 


terant  of  milk,  it  was  formerly  thought  that  such 
adulteration  could  readily  be  detected  by  ascertaining 
the  specific  gravity;  but  the  results  of  using  the  spe- 
cific gravity  may  be  very  misleading,  when  consid- 
ered without  reference  to  any  other  factor. 

INFLUENCE   OF  TEMPERATURE  ON   SPECIFIC 
GRAVITY 

Most  liquids  expand  when  heated  and  contract  when 
cooled.  A  vessel  full  of  milk  or  water  at  40°  F.  will 
overflow  when  heated  considerably  higher,  that  is, 
will  hold  less  of  the  fluid,  and  so  the  same  volume 
weighs  less  at  higher  than  at  lower  temperatures. 
From  this  it  is  readily  seen  that  the  specific  gravity  of 
a  liquid  like  water  or  milk  grows  less  when  its  tem- 
perature increases.  On  the  other  hand,  a  vessel  full 
of  water  at  200°  F.  is  not  full  when  cooled  to  40°  F. 
The  same  weight  of  water  occupies  less  volume  and 
its  specific  gravity  is  higher.  Decrease  of  tempera- 
ture increases  the  specific  gravity  of  liquids.  It  is 
therefore  necessary  in  measuring  the  specific  gravities 
of  different  liquids  to  have  the  measurements  made  at 
the  same  temperature,  if  they  are  to  be  comparable. 
The  temperature  commonly  used  is  60°  F. 

METHOD  OF  TESTING  THE  SPECIFIC  GRAVITY 
OF  LIQUIDS 

The  specific  gravity  of  liquids  is  readily  measured 
by  an  instrument  known  as  a  hydrometer.  The  use 
of  such  an  instrument  is  based  on  the  fact  that,  when 
a  solid  body  floats  in  a  liquid,  it  displaces  an  amount 
of  liquid  equal  in  weight  to  the  weight  of  the  floating 


178  MODERN    METHODS   OF   TESTING   MILK 

body.  Thus  it  sinks  deeper  in  a  light  liquid  than  in 
a  heavy  one,  because  it  takes  a  larger  volume  of  the 
light  liquid  to  equal  the  weight  of  the  floating  body. 
Such  an  instrument  is  graduated  as  the  re- 
sult of  extensive  experiments,  so  that  the 
specific  gravity  of  the  liquid  in  which  the 
hydrometer  is  placed  can  be  read  at  the 
point  where  the  scale  is  even  with  the  upper 
surface  of  the  liquid.  A  hydrometer  is  cor- 
rect only  for  the  temperature  used  in  stand- 
ardizing it.  When  a  hydrometer  has  a 
scale  specially  adapted  to  the  limits  of  the 
specific  gravity  of  milk,  it  is  called  a  lactom- 
eter. Of  the  various  lactometers  made,  only 
two  are  sufficiently  used  to  deserve  atten- 
tion: (i)  The  Quevenne,  and  (2)  the  New 
York  Board  of  Health,  lactometers. 

THE  QUEVENNE  LACTOMETER 

Description. — This  instrument  (Fig.  48) 
is  a  hydrometer  the  scale  of  which  is  di- 
vided into  25  equal  parts,  going  from  15 
to  40.    Each  division  is  called  a  degree,  and 
FIG.  47     every  fifth  degree  is  numbered  on  the  scale. 
LACTOMETER  The  Point  marked   J5  corresponds  to  the 
point  marked  specific  gravity  1.015  on  an 
ordinary  hydrometer,  and  is  the  point  to  which  it  will 
sink  when  placed  in  liquids  whose  specific  gravity  is 
1.015.    The  40  degree  mark  on  the  Quevenne  lactom- 
eter corresponds  to  the  specific  gravity   1.040  mark 
on  a  hydrometer.    The  relation  between  specific  grav- 


TESTING  BY  THE  LACTOMETER  179 

ity  and  the  scale  of  the  Quevenne  lactometer  is  shown 
as  follows: 

SPECIFIC  Reading  of 

GRAVITY  Quevenne  lactometer 

1.015 15 

1.020 20 

1.025 25 

1.030 30 

1.035,  etc 35,  etc 

Corrections  for  temperature. — The  Quevenne  lac- 
tometer is  graduated  to  give  correct  results  at  60°  F. 
When  it  is  used  in  milk,  the  milk  should  be  at  60°  F., 
or,  if  at  some  temperature  above  or  below  60°  F.,  a 
correction  of  the  lactometer  reading  must  be  made. 
This  correction  can  be  closely  made  by  adding  to  the 
lactometer  reading  .1  for  each  degree  above  60°  F., 
or  by  subtracting  .1  for  each  degree  below  60°  F. 
For  more  exact  corrections,  consult  table  on  the  fol- 
lowing page. 

The  Quevenne  lactometer  should  carry  a  thermom- 
eter, the  scale  of  which  is  placed  for  convenience  above 
the  lactometer  scale. 

Process  of  using  Quevenne  lactometer. — The  sam- 
ple of  milk  to  be  tested  for  specific  gravity  is  brought 
to  a  temperature  between  50°  and  70°  F.  For  con- 
venience the  milk  is  placed  in  a  cylinder  (Fig.  49), 
which  is  nearly  filled.  The  lactometer  is  carefully 
lowered  into  the  milk  until  it  floats  and  is  allowed  to 
remain  half  a  minute  or  more.  Then  one  reads  and 
records  (i)  the  point  at  which  the  lactometer  scale 
comes  in  contact  with  the  upper  surface  of  the  milk; 
and  (2)  the  temperature.  The  lactometer  reading  is 


i8o 


I 


I 


h 
_l_ 

fe 

i_ 

fc 


CO 

K 

O 


«  §  w 

§5W 


Old        COCO 


WCOCOCOCOCOCOCOCOCO 


O 
U 


ubi 


TESTING  BY  THE  LACTOMETER  jgl 

then  corrected,  if  the  temperature  is  above  or  below 
60°  F.  For  example,  the  lactometer  settles  in  milk, 
which  is  at  a  temperature  of  65°  F.,  to  the  point 
marked  29.  Adding  to  the  reading  for  correction  .1 
for  each  degree  above  60°  F.,  which  in  this  case  is  .5, 
the  reading  becomes  29.5.  This  means  that  the  spe- 
cific gravity  is  1.0295.  If  Ae  temperature  of  the 
milk  were  55°  F.,  the  correction  is  subtracted  and 
the  reading  becomes  28.5,  equal  to  specific  gravity 
1.0285. 

THE  NEW  YORK  BOARD  OF  HEALTH 
LACTOMETER 

Description. — This  lactometer  has  been  in  common 
use  among  milk-inspectors  in  the  east- 
ern and  middle  states.     Its  scale  is  quite 
different  from  that  of  the  Quevenne  lac- 
tometer, since  it  is  divided  into  120  equal 
parts.     Beginning  at  the  top  of  the  in- 
strument, the  zero  point  on  the  scale  is 
the  point  to  which  the  lactometer  sinks 
in  water;  and  the  point  is  marked  100 
to  which  it  settles  in  milk  of  specific  grav- 
ity 1,029  at  60°  F.   (Quevenne  reading, 
29),  the  lowest  limit  supposed  to  belong 
to  normal  milk.     The  distance  between 
the  zero  and  100  points  is  divided  into 
100  equal  parts  and  the  scale  is  then  pro- 
longed beyond  the  100  mark  for  20  di-       FIG.  48 
visions  to  120.     The  instrument  is  used  CYLINDER  FOR 
in  the  same  way  as  the  Quevenne  lactom-    LACTOMETKR 
eter  in  testing  milk. 


182 


MODERN    METHODS   OF  TESTING   MILK 


l.ooo 

m 
tt 

10-  - 

1.00V 

. 
20-  - 

t.oto- 

,,„ 

• 
- 

so-  - 

'» 

_ 

t.MO- 

€0   • 

- 

10  : 

?0 

10   ^ 

- 

1.025- 

5V 

- 

co- 

- 

4.030 

no- 

:« 

- 

f.035 

oo- 

3V 

40 

• 

. 

01 

1 

Comparison  of 
the  two  lactometer 
scales. — In  compar- 
ing the  scales  of  the 
Quevenne  and  Board 
of  Health  lactom- 
eters, the  following 
points  will  make  clear 
their  relations:  (i) 
The  zero  point  on 
both  instruments  in- 
dicates the  specific 
gravity  of  water, 
that  is,  i.ooo.  (2) 
On  the  B.  of  H.  lac- 
tometer, the  100  di- 
visions or  degrees 
from  o  to  100  corre- 
spond to  29  divisions 
on  the  Quevenne. 
Therefore  one  de- 
gree on  the  B.  of  H. 
lactometer  c  o  r  r  e- 
sponds  to  .29  degree 
on  the  Quevenne.  To 
convert  the  B.  of  H. 
lactometer  reading 
into  that  of  the 
Quevenne,  multiply 
the  reading  of  the 

-Quevenne  lactometer/"  former  by  .29.      The 

relation  of  the  specific  gravity  scale  of  a  hydrometer 


PIG.  49— COMPARISON  OF  DIFFERENT 

SPECIFIC  GRAVITY   SCALES 
Sis  specific  gravity  scale;  Nis  New  York 
Board  01  Health  lactometer;  Q  is 


TESTING  BY  THE  LACTOMETER 


183 


to  the  scales  of  the  Quevenne  and  B.  of  H.  lactometer 
is  shown  in  Fig.  50. 


TABLE  II. — DEGREES  ON  QUEVENNE  LACTOMETER  CORRESPONDING  TO 
DEGREES  ON  NEW  YORK  BOARD  OF  HEALTH  LACTOMETER 


BOARD  OP 
HEALTH 

QUEVENNE 

BOARD  OF 
HEALTH 

QUEVENNE 

BOARD  OF 
HEALTH 

QUEVENNE 

Degrees 

Degrees 

Degrees 

Degrees 

Degrees 

Degrees 

60 

17.4 

81 

23.5 

101 

29.3 

61 

17.7 

82 

23.8 

102 

29.6 

62 

18.0 

83 

24.1 

103 

29.9 

63 

18.3 

84 

24.4 

104 

30.2 

64 

18.6 

85 

24.6 

105 

30.5 

65 

18.8 

86 

24.9 

106 

30.7 

66 

19.1 

87 

25.2 

107 

31.0 

67 

19.4 

88 

25.5 

108 

3J.3 

68 

19.7 

89 

25.8 

109 

81.6 

69 

20.0 

90 

26.1 

110 

31.9 

70 

20.3 

91 

26.4 

111 

32.2 

71 

20.6 

92 

26.7 

112 

32.5 

72 

20.9 

93 

27.0 

113 

32.8 

73 

21.2 

94 

27.3 

114 

33.1 

74 

21.5 

95 

27.6 

115 

33.4 

75 

21.7 

96 

27.8 

116 

33.6 

76 

22.0 

97 

28.1 

117 

33.9 

77 

22.3 

98 

28.4 

118 

34.2 

78 

22.6 

99 

28.7 

119 

34.5 

79 

22.9 

100 

29.0 

120 

34.8 

80 

23.2 

.... 

.... 

.... 

.... 

184  MODERN   METHODS  OF  TESTING   MILK 

Corrections  for  temperature. — In  using  the  B.  of 
H.  lactometer,  correction  is  made  for  temperatures 
above  or  below  60°  F.  For  each  degree  of  tempera- 
ture of  milk  above  60°  F.,  add  .3  to  the  lactometer 
reading,  and  for  each  degree  below  60°  F.  subtract  .3 
from  the  reading. 

PRECAUTIONS  IN  TESTING  SPECIFIC  GRAVITY 
OF  MILK 

1.  Milk  should,  for  best  results,  not  be  examined 
until  i  to  2  hours  or  more  after  milking,  since  the 
specific  gravity  of  milk  is  lower  for  a  while  after  be- 
ing drawn  than  it  is  later,  due  chiefly  to  the  presence 
of  gases. 

2.  The  sample  of  milk  must  be  completely  mixed. 

3.  The  lactometer  must  be  kept  clean. 

4.  In  milk  which  has  been  preserved  by  potassium 
bichromate,  the  specific  gravity  is  about  one  degree 
higher  than  in  the  normal  milk,  in  case  the  usual 
amount  of  bichromate  has  been  added.   (See  p.  30). 

VALUE  OF  LACTOMETER  IN  DETECTING  ADUL- 
TERATED MILK 

The  value  of  the  lactometer  in  detecting  adulterated, 
especially  watered,  milk  was  formerly  overestimated. 
Taken  alone,  the  results  given  by  the  lactometer  may 
be  thoroughly  unreliable  and  misleading.  It  has 
come  to  be  quite  generally  recognized  that  the  proper 
use  of  the  lactometer  in  milk  inspection  is  largely  to 
indicate  whether  a  sample  is  suspicious  and  to  furnish 
a  guide  as  to  whether  it  is  necessary  to  take  a  sam- 
ple for  further  detailed  investigation  by  chemical  anal- 


TESTING  BY  THE  LACTOMETER  185 

ysis.  As  already  stated,  a  milk  which  is  both  skimmed 
and  watered  may  appear  to  be  entirely  normal  by  the 
lactometer. 

METHOD    OF  TESTING  MILK   FOR  SOLIDS   BY 
LACTOMETER 

As  the  result  of  extended  studies  of  the  relations  ex- 
isting between  the  specific  gravity  of  milk,  milk-fat 
and  milk-solids,  rules  have  been  formulated  by  means 
of  which  it  is  possible  to  calculate  with  a  close  degree 
of  approximation  the  total  solids  of  milk,  when  one 
knows  the  percentage  of  fat  and  the  (Quevenne)  lac- 
tometer reading. 

Babcock's  formulas  for  solids  and  solids-not-fat.  — 
The  following  formulas  were  devised  by  Dr.  Bab- 
cock: 

(1)  Formula  for  determining  solids-not-fat.  —  Sol- 
ids-not-fat=j4L-K2f,   in  which   L  is  the  reading  of 
the  Quevenne  lactometer  and  f  is  the  per  cent,  of  fat 
in  the  milk. 

(2)  Formula  for  determining  solids  in  milk.  —  Total 


These  formulas  can  be  expressed  in  the  form  of 
rules  as  follows: 

Rule  i.  —  To  find  the  per  cent,  of  solids-not-fat  in 
milk,  divide  the  reading  of  the  Quevenne  lactometer 
by  4,  and  to  the  result  add  the  per  cent,  of  fat  in  the 
milk  multiplied  by  .2. 

Rule  2.  —  To  find  the  per  cent,  of  solids  in  milk,  di- 
vide the  Quevenne  lactometer  reading  by  4,  and  to 
the  result  add  the  per  cent,  of  fat  multiplied  by  1.2. 

Examples:  —  A  milk  containing  4  per  cent,  of  fat 


186 


MODERN    METHODS  OF  TESTING   MILK 


shows  a  lactometer  reading  of  32.  What 
is  the  per  cent,  (a)  of  solids-not-fat,  (b) 
of  total  solids? 

(a)  The  lactometer  reading  (32),  di- 
vided by  4,  equals  8.  The  per  cent,  of 
fat  (4),  multiplied  by  .2,  equals  .8.  Add- 
ing 8  and  .8,  we  obtain  8.8  as  the  per 
cent,  of  solids-not-fat. 

b)  The  per  cent,  of  total  solids  in  the 
milk  is  12.8  per  cent.;  for  the  lactometer 
reading,  divided  by  4,  equals  8,  the  per 
cent,  of  fat  (4)  multiplied  by  1.2  equals 
4.8,  and  8  plus  4.8  equals  12.8. 

Richmond's  slide-rule  for  calculating 
solids. — Instead  of  going  through  the 
details  of  calculation  to  estimate  solids 
in  milk,  Richmond  uses  a  slide-rule  which 
is  a  clever  mechanical  calculating  device. 
(Fig.  51).  The  results  obtained  in  this 
manner  agree  closely  with  those  given  by 
Babcock's  formulas.  The  method  of 
using  the  slide-rule  is  as  follows:  De- 
termine (i)  the  Quevenne  lactometer 
reading,  (2)  the  temperature  of  the 
milk,  and  (3)  the  per  cent,  of  fat  in  the 
milk.  Then  set  the  central  slide  of  the 
rule  so  that  the  observed  lactometer  read- 
ing is  opposite  the  60  degree  (tempera- 
ture) mark.  The  true  lactometer  read- 
ing is  found  opposite  the  line  indicating 
the  observed  temperature  of  the  milk.  Having  thus 
corrected  the  lactometer  reading  for  temperatures 


FIG.  50 
RICHMOND'S 

SLIDE-RULE 


TESTING  BY  THE  LACTOMETER  187 

other  than  60°  F.,  next  set  the  arrow  on  the  sliding 
'portion  of  the  rule  opposite  the  per  cent,  of  fat  found 
in  the  milk  and  read  the  total  solids  contained  in  the 
milk  corresponding  with  the  corrected  lactometer  read- 
ing or  specific  gravity. 

To  illustrate,  suppose  the  lactometer  reading  of  2 
sample  of  milk  at  70°  F.  is  30  and  the  per  cent,  of  fat 
is  4.  To  correct  for  temperature  and  find  what  the 
lactometer  reading  would  be  at  60°  F.,  the  lactometer 
reading  (30)  is  placed  opposite  the  little  arrow  at  60 
on  the  temperature  scale.  Then,  looking  at  the  point 
of  temperature  70,  we  find  opposite  this  point  31.3, 
which  is  the  corrected  or  true  reading.  Next,  we 
place  the  arrow  opposite  the  4  per  cent,  mark,  as  the 
milk  contains  4  per  cent,  of  fat,  and  then  notice  where 
the  point  31.3  (specific  gravity),  comes  in  contact  with 
the  solids  scale.  It  corresponds  closely  to  12.8,  which 
is  the  per  cent,  of  total  solids  in  the  sample  of  milk 
examined.  Some  practice  with  this  slide-rule  enables 
one  to  work  rapidly. 

Specific  gravity  of  milk-solids. — The  following  rule 
has  been  proposed  by  Fleischmann  for  calculating  the 
specific  gravity  of  milk-solids :  Multiply  the  specific 
gravity  of  the  milk  by  100,  from  the  result  subtract 
100  and  divide  this  result  by  the  specific  gravity  of 
the  milk.  Subtract  the  last  result  from  the  per  cent, 
of  total  solids  in  the  milk  and  then  divide  by  this  re- 
sult the  per  cent  of  total  solids  of  the  milk.  This  may 
also  be  expressed  by  the  following  formula : 


Sp.  gr.  milk-solids= 


milk-solids 


milk-solids— (looXsp.  gr.)— 100 
sp.  gr. 


l88  MODERN    METHODS   OF   TESTING   MILK 

Example  :  A  sample  of  milk  contains  12.5  per  cent. 
of  solids  and  has  a  specific  gravity  of  1.031  ; 
—  what  is  the  specific  gravity  of  the  milk-solids? 

-=-3^-9.494-,   -'.3* 


This  calculation  may  assist  in  determining  whether 
a  sample  of  suspected  milk  has  been  adulterated.  The 
variations  of  the  specific  gravity  of  milk-solids  is  slight, 
ranging  between  1.25  and  1.34.  Milks  richer  in  fat 
have  solids  of  lower  specific  gravity.  The  specific 
gravity  of  milk-solids  is  not  changed  by  watering  milk, 
but  is  increased  by  removing  fat  or  by  addition  of 
skimmed  milk.  Hence,  milk  whose  solids  have  a 
specific  gravity  above  1.34  is  suspected  of  being 
skimmed,  while  a  specific  gravity  above  1.40  is  re- 
garded as  clear  evidence  of  skimming. 


CHAPTER  XIV 

t 

Methods  of  Testing  Milk  for  Casein 

Until  quite  recently  there  have  not  been  available 
simple  methods  for  the"  determination  of  casein  in 
milk.  Two  methods  are  now  in  use :  one  of  them  re- 
sembles somewhat  the  process  used  in  determining 
acidity  in  milk,  employing  the  principle  of  neutraliza- 
tion and  titration  with  alkali ;  while  the  other  pre- 
cipitates the  casein  and  collects  it  by  centrifugal  force 
in  a  graduated  tube. 


VOLUMETRIC  TEST  FOR  CASEIN 

This  method  was  worked  out  at  the  New  York 
State  experiment  station  (Technical  Bulletin  No.  10) 
.by  Van  Slyke  and  Bosworth.  In  outline,  the  method 
is  as  follows:  Into  a  200  cc.  flask  measure  17.5  cc.  (18 
grams)  of  milk,  add  about  80  cc.  of  water  and  I  cc. 
of  phenolphthalein,  after  which  run  in  a  solution  of 
sodium  hydroxide  (caustic  soda)  until  the  mixture  is 
neutral.  Standardized  acetic  acid  is  then  added  until 
the  casein  is  completely  precipitated,  the  volume  of  the 
mixture  is  made  up  to  200  cc.  by  addition  of  water 
and  the  whole  is  then  filtered.  Into  100  cc.  of  the  clear 

189 


IpO  MODERN  METHODS  OF  TESTING  MILK 

filtrate,  standardized  sodium  hydroxide  solution  is  run 
until  neutral.  The  solutions  are  so  standardized  that 
i  cc.  is  equivalent  to  i  per  cent,  of  casein  in  the  milk 
examined.  Therefore,  the  number  of  cubic  centi- 
meters of  standard  acid  used,  divided  by  2,  less  the 
amount  of  standard  alkali  used  in  the  final  titration 
gives  the  percentage  of  casein  in  milk.  The  operation 
usually  requires  12  to  15  minutes  when  apparatus  and 
solutions  are  at  hand  in  convenient  form  ready  for  use ; 
several  determinations  can  be  carried  on  at  the  same 
time  to  advantage. 

Apparatus. — Most  of  the  apparatus  is  such  as  is  in 
common  use  in  dairy  work  in  acidity  testing  (p.  131). 

(1)  Two   SQ-CC.   burettes  accurately   graduated   to 
one-twentieth  cubic  centimeters.     Automatic  burette- 
fillers  save  much  time. 

(2)  Flasks,  volumetric,  holding  200  cc.  and  accu- 
rately marked.     For  greatest  convenience,  flasks  hav- 
ing necks  4^2  to  5  inches  long  and  £4  inches  inside 
diameter  are  preferable. 

(3)  Pipette    (Babcock-test  form),   accurately  gra- 
duated to  deliver  17.5  cc.  (18  grams)  of  milk. 

(4)  Pipette  graduated  to  deliver  100  cc. 

(5)  Pipette  graduated  to  deliver  about  i  cc,  and 
provided  with  a  rubber  bulb  (so-called  dropper). 

(6)  Cups,  plain  white,  holding  200  cc.  or  more. 

(7)  Funnels,  glass  or  granite-ironware,  3  to  4  inches 
in  diameter. 

(8)  Filter-papers  cut  round,  6  to  7  inches  in  dia- 
meter; or  filters  of  fine  linen  cut  to  proper  size  and 
shape,  which  can  be  used  repeatedly,  being  thoroughly 
washed  each  time. 


METHODS   OF  TESTING    MILK    FOR   CASEIN         19! 

(9)  Measuring-cylinders,  accurately  graduated  and 
holding  1000  cc. 

Solution. — Three  solutions  are  used:  (i)  Sodium 
hydroxide,  (2)  acetic  acid  and  (3)  phenolphthalein. 

(1)  Sodium  hydroxide  (caustic  soda).     This  solu- 
tion is  most  conveniently  prepared  by  purchasing  from 
a  reliable  chemical-supply  house  the  standard  normal 
solution  and  then  diluting  exactly  100  cc.  of  this  to 
1260  cc.  (or  79.5  cc.  to  1000  cc.),  using  pure  distilled 
water,  if  possible,  or  else  as  pure  rain  water  as  is  ob- 
tainable.    Alkali   solutions  must  be  kept   in  tightly- 
stopperel  bottles  (p.  138).    "Alkaline  tablets"  (p.  142) 
cannot  be  used  for  the  casein  test. 

(2)  Acetic  acid.    This  solution  is  so  made  that  i  cc. 
will  neutralize  i  cc.  of  the  alkali  solution.    The  simplest 
method  of  preparation  is  to  purchase  a  standard  nor- 
mal solution  and  dilute  100  cc.  to  1260  cc.  (or  79.5  cc. 
to  1000  cc.).     Add  a  small  amount  of  dry  mercuric 
chloride  (corrosive  sublimate)  to  prevent  fermentation, 
and  keep  the  solution  in  tightly-stoppered  bottles. 

(3)  Phenolphthalein.     Dissolve  i  gram  of  the  dry 
powder  in  100  cc.  of  50  per  cent,  alcohol,  adding  one 
or  more  drops  of  dilute  alkali  until  the  solution  is  very 
slightly  pinkish  in  color. 

Performing  the  test. — For  convenience,  the  pro- 
cess can  be  divided  into  six  stages  or  operations:  (i) 
Measuring  and  diluting  sample  of  milk,  (2)  neutraliz- 
ing the  milk,  (3)  precipitation  of  casein,  (4)  filtration 
of  casein,  (5)  titration  with  alkali,  (6)  calculation  of 
results. 

(i)  Measuring  and  diluting  sample  of  milk.  The 
milk  to  be  tested  is  well  mixed  and  a  17.6  cc.  pipette 


IQ2  MODERN  METHODS  OF  TESTING  MILK 

filled  to  the  mark  and  the  milk  run  into  a  2oo-cc.  flask. 
To  this  is  added  about  80  cc.  of  pure,  soft  water,  pre- 
ferably distilled. 

(2)  Neutralizing  the  milk.  To  the  diluted  milk  add 
i  cc.  of  phenolphthalein  solution  and  then  run  into  it 
the  alkali  solution  from  the  burette,  in  small  portions, 
shaking  vigorously  after  each  addition,  until  a  faintly 
but  distinctly  pinkish  shade  of  color  remains  even  after 
considerable  agitation.  Marked  excess  of  alkali  must 
be  avoided.  In  this  connection,  the  preparation  and 
use  of  a  color-standard  are  desirable. 

(a)  Preparation  of  a  color-standard. — More  satisfac- 
tory results  in  neutralizing  can  be  attained  by  prepar- 
ing a  color-standard  for  comparsion,  as  follows :  About 
20  cc.  of  fresh  skim-milk  and  80  cc.  of  water  are  put 
into  a  2OO-CC.  flask  and  a  small  amount  of  corrosive 
sublimate  added  to  prevent  souring.  A  few  drops  of 
ordinary  carmine  ink  are  considerably  diluted  with 
water  and  this  is  carefully  added,  a  few  drops  at  a  time, 
to  the  diluted  skim-milk  until  a  faint  but  distinct  pink- 
ish coloration  appears.  This  can  be  more  readily  and 
accurately  perceived  by  placing  beside  the  flask  another 
flask  half  full  of  uncolored  diluted  skim-milk.  The 
coloration  must  be  as  slight  as  possible  and  yet  be  ap- 
preciably distinct  when  compared  with  uncolored  milk. 
After  the  color-standard  has  been  prepared,  the  flask 
is  stoppered.  It  is  well  to  keep  this  standard  in  a  dark 
place  when  not -in  use.  With  some  carmine  colors,  the 
pinkish  shade  in  the  milk  deepens  on  standing  espe- 
cially when  exposed  to  light,  and  with  others  it  may 
fade.  -  If  at  any  time  a  deeper  shade  is  observed,  the 
proper  shade  can  be  reproduced  by  slight  dilution 


METHODS    OF   TESTING    MILK    FOR   CASEIN         193 

with  skim-milk ;  in  case  of  fading,  the  addition  of  one 
or  more  drops  of  carmine  ink  is  needed.  Skim-milk 
is  used  to  avoid  the  presence  of  fat  which,  in  case  of 


a 


FIG  51  —  APPARATUS   AND  REAGENTS   REQUIRED   IN   THE   NEW  YORK 
STATE  STATION  VOLUMETRIC  CASEIN  TEST 

whole  milk,  separates  on  standing,  adheres  to  the  sides 
of  the  flask  and  obscures  the  color. 

(b)  Use  of  color-standard.  —  In  neutralizing  a 
sample  of  milk,  the  color-standard  is  placed  beside  the 
sample  under  examination  for  constant  comparison 
after  each  addition  of  alkali.  The  flasks  should  be 
placed  on  a  white  surface  and  in  a  good  light.  In  fresh 
milks,  it  is  usually  found  that  3  or  4  cc.  of  alkali  is 


194  MODERN  METHODS  OF  TESTING  MILK 

sufficient  to  make  the  milk  neutral.  One  can  usually 
add  2  or  3  cc.  of  alkali  at  the  start  and  then  add  it  in 
smaller  portions,  until  the  milk  begins  to  show  signs  of 
neutrality,  after  which  the  alkali  is  added  a  drop  at  a 
time. 

(3)  Precipitation  of  casein.  This  step  of  the  pro- 
cess needs  to  be  considered  in  relation  to  the  addition 
of  acid  and  temperature. 

(a)  Addition  of  acid. — Into  the  neutralized  sample 
of  diluted  milk,  which  should  be  at  a  temperature  of 
60°  to  80°  F.,  one  now  runs  from  a  burette  some  of  the 
standardized  acetic  acid,  adding  the  acid  approximately 
in  5  cc.  portions  and  agitating  vigorously  for  a  few  se- 
conds after  each  addition.     It  is  usually  safe  to  add 
about  25  cc.  of  acid  before  examining  the  milk  to  see 
if  the  casein  separates  in  the  form  of  white  flakes. 
After  adding  20  to  25  cc.  and  shaking,  the  mixture  is 
allowed  to  come  to  rest.    If  enough  acid  has  been  ad- 
ded, the    casein    separates    promptly    in    large,  white 
flakes,  and,  on  standing  a  short  time,  the  liquid  above 
the  settled  casein  appears  clear  and  not  at  all  milky. 
If  the  addition  of  25  cc.  of  acid  is  insufficient  to  sepa- 
rate the  casein  properly,  add  I  cc.  more  of  acid  and 
shake;  continue  the  addition  of  acid,  I  cc.  at  a  time, 
until  the  casein  is  observed  to  separate  promptly  and 
completely  on  standing  at  rest  a  short  time.    The  num- 
ber of  cubic  centimeters  of  acid  used  to  effect  precipi- 
tation is  noted  and  this  result  is  recorded  as  A. 

(b)  Influence  of  temperature. — For  convenience  of 
work  and  uniformity  of  results,  the  temperature  of 
the  mixture  at  the  time  of  the  addition  of  acid  may  be 
between  60°  and  80°  F.    Under  these  conditions,  many 


METHODS   OF  TESTING    MILK    FOR   CASEIN         195 

milks  give  satisfactory  results  with  30  cc.  of  acid.  In 
case  of  milk  containing  3.5  to  4  per  cent,  of  casein,  35 
to  45  cc.  of  acid  may  be  needed.  The  amount  of  acid 
may  be  3  to  5  cc.  in  excess  of  that  required  to  effect 
complete  precipitation  without  affecting  appreciably  the 
accuracy  of  the  results,  provided  the  temperature  of 
the  mixture  is  below  80°  F.  In  working  at  tempera- 
tures under  65°  F.,  the  casein  separates  more  slowly 
or  requires  more  acid  to  separate  promptly;  in  such 
cases,  it  is  well  to  use  for  dilution  water  that  is  at  a 
temperature  of  80°  to  85°  F. 

(4)  Filtration  of  casein.  After  the  casein  is  com- 
pletely precipitated,  pure,  soft  water  (preferably,  dis- 
tilled) is  added  until  the  200  cc.  is  reached.  The 
flask  is  then  vigorously  shaken  10  or  15  seconds,  in 
order  to  make  the  distribution  of  acid  through  the  mix- 
ture as  uniform  as  possible.  The  contents  of  the  flask 
are  then  poured  on  a  dry  filter  and  the  filtrate  caught 
in  a  cup.  The  funnels,  filters  and  cups  should  all  be 
dry  before  being  used.  It  is  well  generally  to  allow  the 
filtration  to  continue  until  practically  all  of  the  liquid 
has  run  into  the  cup.  Two  points  deserve  attention  in 
this  connection,  (i)  the  rapidity  of  filtration  and  (2) 
the  appearance  of  the  filtrate. 

(a)  Rapidity  of  filtration. — The  usual  time  of  filtra- 
tion should  not  exceed  3  to  5  minutes.  The  rapidity 
depends  upon  the  temperature  of  precipitation  and  the 
completeness  of  the  separation  of  casein.  In  general, 
the  higher  the  temperature  of  the  mixture  when  pre- 
cipitated with  acid,  the  more  rapid  should  be  the  filtra- 
tion, other  conditions  being  uniform.  In  case  of  insuffi- 
cient acid,  the  filtration  is  slower. 


196  MODERN  METHODS  OF  TESTING  MILK 

(b)~  Appearance  of  filtrate. — The  filtrate  should  be 
quite  clear,  though  this  is  not  always  a  sure  indication 
that  the  right  amount  of  acid  has  been  used.  Some- 
times the  filtrate  may  be  clear  when  not  quite  enough 
acid  has  been  added,  in  which  case  the  filtration  is 
usually  slow.  In  case  of  milks  rich  in  fat,  a  slight  tur- 
bidity may  appear,  due  to  fat-globules  in  the  filtrate. 
The  filtrate  should  be  free  from  all  signs  of  marked 
turbidity  or  anything  like  milkiness.  If  such  a  filtrate 
appears,  a  new  sample  of  milk  should  be  taken  and  the 
operation  repeated  from  the  beginning,  more  acid  be- 
ing used  than  before.  With  a  little  experience,  espe- 
cially under  proper  instruction,  no  difficulty  should  be 
found  in  recognizing  quickly  when  the  casein  is  sepa- 
rated so  as  to  give  satisfactory  results. 

(5)  Titration  with  alkali.  After  filtration  is  com- 
pleted, one  measures  100  cc.  of  the  filtrate  with  the 
pipette  into  a  cup  and  then  from  the  burette  runs  into 
this  the  standard  alkali  until  a  faint,  but  distinct,  pink 
color  remains  clearly  marked  through  the  solution  for 
half  a  minute  or  longer  before  beginning  to  fade.  The 
number  of  cubic  centimeters  of  alkali  used  is  noted  and 
this  result  is  recorded  as  B. 

The  last  portions  of  alkali  must  be  added  carefully, 
a  drop  at  a  time,  agitating  the  mixture  well  after  each 
addition.  The  exact  neutral  point  is  not  perfectly 
sharp  on  account  of  the  presence  of  phosphates,  and 
the  apppearance  of  the  desired  coloration  is,  therefore, 
not  as  sudden  and  pronounced  as  might  be  desired. 
With  experience  one  should  have  no  difficulty  in  get- 
ting within  one  drop  of  the  correct  amount  of  alkali. 
The  chief  precaution  to  be  observed  is  to  have  the  same 


METHODS    OF   TESTING    MILK    FOR   CASEIN 


shade  and  duration  of  color  every  time.  Thus  one 
should  not  in  one  titration  add  alkali  until  a  deep  pink 
coloration  appears,  lasting  for  some  minutes,  and  then 
in  another,  a  coloration  that  disappears  within  5  se- 
conds. 

(6)  Calculation  of  results.  —  The  method  of  obtain- 
ing the  percentage  of  casein  is  very  simple:  Divide 
by  2  the  number  of  cubic  centimeters  of  acid  used  (A) 
and  from  the  result  subtract  the  number  of  cubic  centi- 
meters of  alkali  used  (B)  in  neutralizing  100  cc.  of 
filtrate;  or,  expressed  more  briefly,  divide  A  by  2  and 
from  the  result  subtract  B.  Expressed  as  a  formula 
this  becomes:  (A-f-2)  —  B=Per  cent,  of  casein  in  milk. 

Example:  One  uses  30  cc.  (A)  of  acid  in  precipi- 
tating casein  and  11.95  cc.  (B)  of  alkali  in  neutralizing 
100  cc.  of  filtrate  (one-half  of  filtrate  from  the  casein 
precipitate,  corresponding  to  9  grams  of  milk).  Sub- 
stituting 30  for  A  and  11.95  f°r  ^  m  tne  formula,  we 
have  (30-7-2)—  11.95=15—  11.95=3.05  (per  cent,  of 
casein  in  milk). 

Use  of  preservatives.  —  In  making  a  casein  deter- 
mination by  this  method,  it  is  desirable  when  possible 
to  use  milk  not  more  than  24  hours  old,  which  has  been 
kept  in  a  cool  place.  Milk  which  is  sour  or  which  coag- 
ulates on  heating  can  not  be  used  with  satisfactory 
results.  However,  by  adding  to  fresh  milk  powdered 
mercuric  chloride  (corrosive  sublimate)  in  the  approxi- 
mate proportion  of  I  part  to  1,000  or  1,500  parts  of 
milk,  and  then  keeping  the  mixture  at  a  temperature  of 
50°  F.  or  lower,  one  can  obtain  satisfactoiy  results  with 
milk  that  had  been  kept  2  to  3  weeks.  Milk  thus  treated 
should  be  shaken  often  enough  to  keep  the  fat  well 


I9o  MODERN  METHODS  OF  TESTING  MILK 

incorporated  in  the  body  of  the  milk.  The  desired 
amount  of  mercuric  chloride  may  be  approximately 
measured  by  taking  the  quantity  that  will  easily  lie  on 
the  surface  of  a  silver  dime  for  one  quart  of  milk  or, 
more  conveniently,  the  amount  held  by  a  o.22-inch,  pis- 
tol cartridge-shell  ^  inch  long,  when  loosely  filled. 
A  stiff  wire  soldered  to  such  a  shell  makes  it  conven- 
ient to  handle.  Commercial  mercuric  chloride  tablets 
containing  color-matter  can  not  be  used. 

Summary  of  Precautions. — Below  we  give  in  out- 
line the  special  points  to  be  observed  with  care  in  per- 
forming the  operations  of  the  test,  assuming  that  the 
graduated  glassware  is  accurate  and  the  solutions  of 
correct  strength. 

(1)  Preliminary  neutralization.     In  the  neutraliza- 
tion of  the  sample  of  milk,  excess  of  alkali  must  be 
avoided ;  this  can  be  controlled  by  the  use  of  a  properly 
prepared  color-standard. 

(2)  Conditions  of  precipitation.     Before  precipitat- 
ing with  acid,  have  the  dilute,  neutralized  milk  at  a 
temperature  between  60°  and  80°  F.    Add  enough  acid 
to  cause  the  casein  to  separate  promptly  in  large  flakes,, 
leaving  the  supernatant  liquid  clear.    Shake  the  mixture 
vigorously  at  intervals  during  the  addition  of  acid; 
also  after  complete  precipitation  and  again  after  dilu- 
tion to  the  200  cc.  mark. 

(3)  Filtration.     Allow  most  of  the  liquid  to  run 
through  the  filter  before  making  the  final  titration  with 
alkali. 

(4)  Titration  with  alkali.     In  titrating  the  filtrate 
with  alkali,  avoid  an  excess  of  alkali.    Add  the  alkali 
solution  cautiously  until,  after  thorough  agitation,  a 


METHODS  OF  TESTING  MILK  FOR  CASEIN 


faint  but  distinct  pink  color  remains  through  the  solu- 
tion half  a  minute  or  longer.  The  same  uniform  shade 
and  duration  of  pink  color  should  be  obtained  as  near- 
ly as  possible  in  all  cases. 

(5)  Acid  milk.  Milk  that  is  sour  or  that  coagulates 
on  heating  should  not  be  used. 

(6)  Use  of  preservatives.    Milk  treated,  when  fresh, 
with  a  small  amount  of  powdered  mercuric  chloride 
and  then  kept  in  a  cool  place  gives  good  results  for 
two  or  three  weeks. 

CENTRIFUGAL  TEST  FOR  CASEIN 

The  following  method  has  been  devised  at  the  Wis- 
consin experiment  station  (Bulletin  156)  by  Hart: 

Apparatus  and  Reagents.  —  (i)  Testing-tubes  with 
neck  so  graduated  that  each  division  represents  0.2  per 
cent,  when  a  5-cc.  sample  of  milk  is  used.  (2)  Centri- 
fuge of  special  form,  run  by  hand,  having  a  wheel  15 
inches  in  diameter  and  geared  to  give  a  speed  of  2000 
revolutions  a  minute.  (3)  Pipette  for  measuring  5  cc. 
of  milk.  (4)  Cylinder  for  measuring  2  cc.  of  chloro- 
form. (5)  Dilute  acetic  acid  containing  0.25  per  cent. 
prepared  by  diluting  10  cc.  of  glacial  acetic  acid  to  100 
cc.  with  water,  and  then  diluting  25  cc.  of  this  solu- 
tion to  1000  cc.  (6)  Chloroform  of  the  best  quality. 

Method  of  operating  test.  —  In  a  testing-tube  one 
puts  2  cc.  of  chloroform  and  on  top  of  this  20  cc.  of 
the  dilute  acid.  Milk  (65°  to  75°  F.)  is  then  run  in, 
after  which  the  thumb  is  placed  over  the  opening  of 
the  tube  which  is  then  inverted  to  bring  the  mixture 
into  the  barrel-shaped  portion  ;  then  the  whole  is  shaken 
with  considerable  vigor  for  15  to  20  seconds,  accurately 


2OO  MODERN    METHODS  OF  TESTING   MILK 

timed  with  watch  under  the  eye.  The  tubes  are  then 
placed  in  the  centrifuge  within  20  minutes  and  whirled 
7}4  to  8  minutes  at  a  speed  of  2000  revolutions  a 
minute.  This  must  be  done  with  such  precision  that  the 
use  of  a  metronome  is  recommended  as  important  dur- 
ing the  whirling.  The  whirling  done,  the  tubes  are  re- 
moved and  placed  in  an  upright  position  in  a  rack  and 
then  read  after  10  minutes  or  more.  The  end  surfaces 
of  the  cylindrical  mass  of  casein  should  be  flat ;  the  re- 
sult in  per  cent,  of  casein  is  read  directly  on  the  scale. 
Fresh  milk  is  desirable,  but  it  is  said  that  7-day  com- 
posite samples  may  be  used  by  taking  i -ounce  samples 
of  milk  daily,  in  a  brown  or  amber-colored  bottle,  ad- 
ding on  the  first  and  third  days  i*^  to  2  grains  of  bi- 
chromate (one-fourth  ordinary  tablet).  This  test  de- 
mands more  than  ordinary  exactness  of  manipulation. 


CHAPTER   XV 

Methods  oi  Testing  Milk  and  Milk  Products 
for  Adulterations 

Milk  is  commonly  adulterated  in  one  of  the  follow- 
ing ways:  (i)  By  addition  of  water,  (2)  by  removal 
of  fat  (skimming)  or  addition  of  skim-milk,  (3)  by 
addition  of  substances  not  normally  found  in  milk, 
such  as  preservatives  and  coloring  matter.  All  these 
forms  of  adulteration  may  occur  in  the  same  milk. 

DETECTION  OF  ADDED  WATER  IN  MILK 

Since  water  in  milk  is  the  same  chemical  compound 
as  the  water  found  everywhere  else,  it  is  impossible 
to  identify  added  water  in  milk  by  any  direct  test  for 
special  properties.  The  presence  of  added  water  in 
milk  can  be  learned  with  certainty  only  by  indirect 
means  and  even  then  not  with  certainty  in  all  sus- 
pected cases.  An  examination  of  milk  direct  from 
the  cow  or  herd,  when  this  is  possible,  may  settle  the 
question  of  watering.  The  lactometer,  while  unrelia- 
ble as  a  sure  means  of  detecting  added  water  in  milk, 
may  give  a  helpful  suggestion,  used  as  a  preliminary 
test.  Thus,  if  a  milk  shows  a  specific  gravity  under 
1.028,  it  is  open  to  the  suspicion  of  being  watered,  and 
should  then  be  carefully  examined  in  other  ways. 

Most  states  fix  legal  standards  for  the  per  cent,  of 
water,  solids,  fat,  and  solids-not-fat  in  milk,  and  any 

201 


2O2  MODERN    METHODS   OF   TESTING   MILK 

milk  falling  below  the  fixed  limit  in  composition  is 
regarded  as  adulterated.  Thus,  a  standard  common 
to  several  states  is  12  per  cent,  of  solids  and  3  per  cent, 
of  fat.  This  means  also  that  such  legal-standard  milk 
must  not  contain  more  than  88  per  cent,  of  water  or 
less  than  9  per  cent,  of  solids-not-fat. 

The  relations  of  the  different  constituents  of  milk 
have  been  studied  and  formulas  have  been  devised 
which  enable  one  in  an  approximate  way  to  tell  how 
much  water  has  been  added  to  a  sample  of  milk  be- 
yond the  amount  allowed  by  the  standards.  These 
formulas  are  based  on  the  assumption  that  the  limits 
fixed  by  the  legal  standard  represent  the  lowest 
amounts  of  solids  and  fat  found  in  normal  milk,  and 
they  are  correct  only  when  the  original  milk  contains 
the  lowest  percentages  given  in  the  legal  standard. 

In  calculating  the  amount  of  added  water  in  milk, 
the  amount  of  solids-not-fat  (total  solids  minus  fat) 
is  used  as  a  basis.  The  procedure  is  as  follows : 

(1)  Determine  the  per  cent,  of  fat  in  the  suspected 
sample. 

(2)  Take  the  lactometer  (Quevenne)  test. 

(3)  Determine   the   amount   of   solids-not-fat   ac- 
cording to  the  formula,  %L+.2i.  (p.  137). 

(4)  Apply  the  following  rule:  Multiply  the  per  cent, 
of  solids-not-fat  by  100  and  divide  the  result  by  the 
legal   standard   for  solids-not-fat.     .Subtract  the  last 
result  from  100  and  the  result  is  the  per  cent,  of  ad- 
ded water  in  the  sample  of  suspected  milk.    This  rule 
is  expressed  in  the  form  of  the  following  formula: 

per  cent,  of  solids-not-fat  X  100. 
Per  cent,  of  added  water=ioo-legal  standard  for  solids-not-f at. 


TESTING  MILK  FOR  ADULTERATIONS  2O3 

This  formula  gives  only  the  amount  of  water 
added  beyond  the  limit  fixed  by  the  legal  standard 
and  is  correct  only  if  the  original  milk  contained  the 
amount  of  solids-not-fat  prescribed  by  the  standard 
(usually  9  per  cent.).  Hence,  in  cases  of  watered 
milk,  the  calculated  amount  of  water  added  is  gener- 
ally less  than  the  real  amoun)t  added. 

Example  :  A  milk  is  found  to  contain  3  per  cent,  of 
fat  and  to  show  a  lactometer  reading  of  27.  Applying 
the  formula  for  finding  the  amount  of  solids-not-fat, 
the  per  cent,  is  7.35.  If  the  legal  standard  for  solids- 
not-fat  is  9,  then  the  formula  becomes 

ioo 


the  per  cent,  of  added  water  that  is  contained  in  the 
milk,  assuming  that  it  contained  9  per  cent,  of  solids- 
not-fat  before  being  watered. 

The  following  rule  can  also  be  used:  Add  together 
the  lactometer  reading  and  the  per  cent,  of  fat  present 
in  the  milk,  divide  the  sum  by  36,  multiply  the  result 
by  ioo  and  subtract  the  last  result  from  ioo.  Ex- 
pressed as  a  formula,  this  becomes 

fdCLd  water  M*  milk~icx>-lactometer  ^ading+pe  r  cent,  of  fat^^ 

An  examination  of  the  serum  of  milk  by  means  of 
a  refractometer  gives,  probably,  the  most  reliable 
means  of  detecting  added  water  in  milk,  but  this 
method  is  available  only  for  special  workers.  For  its 
details  see  "Food  Inspection  and  Analysis,"  by  Leach, 
(P-  139)- 


2O4  MODERN    METHODS   OF   TESTING   MILK 

DETECTION  OF  SKIMMED  MILK 

The  percentage  of  fat  in  milk  in  relation  to  the 
other  milk-solids  is  reduced  either  (i)  by  direct  re- 
moval of  fat  through  some  process  of  skimming  or 
(2)  by  the  addition  of  separator  skim-milk  to  nor- 
mal milk.  Milk  containing  less  than  3  per  cent,  of 
fat  is  generally  skimmed.  Watering  milk  does  not 
disturb  the  relations  of  the  constituents  of  milk  to 
one  another,  since  it  reduces  the  percentages  of  all 
uniformly,  but  the  removal  of  fat  does  very  seriously 
affect  the  amounts  of  the  constituents  in  respect  to 
their  relative  percentages.  In  skimming  milk,  the 
solid  constituent  most  largely  removed  is  fat,  com- 
paratively little  casein,  sugar,  etc.,  being  taken  with 
the  fat.  The  removal  of  fat  therefore  leaves  the  milk 
containing  less  fat  but  with  most  of  its  casein,  sugar, 
etc.,  still  remaining.  In  normal  herd  milk,  containing 
over  3  per  cent,  of  fat,  the  percentage  of  fat  is  rarely 
as  low  as  the  percentage  of  casein  and  albumin.  In 
5,500  analyses  of  samples  of  American  milks,  compiled 
by  the  author,  with  a  fat  content  lying  between  3  and 
5  per  cent.,  the  fat  averages  3.92  per  cent.,  and  the  ca- 
sein and  albumin  together,  3.20  per  cent. ;  that  is,  for  I 
part  of  casein  and  albumin  there  is  an  average  of 
1.225  parts  of  fat.  In  skimming  such  milk,  the  fat  may 
be  decreased  to  I  per  cent,  or  .1  per  cent.,  but  the  re- 
maining milk  still  contains  about  3.20  per  cent,  of 
casein*  and  albumin.  Milk  is  open  to  the  suspicion  of 
being  skimmed,  when  the  percentage  of  fat  falls  be- 
low that  of  the  casein  and  albumin. 

The  percentage  of  fat  removed,  based  OP  the  legal 


TESTING  MILK  FOR  ADULTERATIONS  205 

standard,  may  be  calculated  by  the  following  rule: 
Multiply  the  per  cent,  of  fat  in  the  milk  by  100,  di- 
vide the  result  by  the  legal  standard  for  fat  and  sub- 
tract this  from  100;  or  expressed  as  a  formula: 

The  per  cent,  of  fat  removed=ioo — F  x  I0°      This 

3. 
formula  is  true  only  for  milks  originally  containing  3 

per  cent,  of  fat  and  so  its  results  are  generally  much 
below  the  truth.  For  example,  in  a  milk  containing 
originally  5  per  cent,  of  fat,  which  has  been  skimmed 
to  2.50  per  cent.,  thus  removing  50  per  cent,  of  the 
fat  in  the  milk,  the  above  formula  would  indicate  that 
only  16.6  per  cent,  of  the  fat  had  been  removed.  In 
most  cases  results  nearer  the  actual  truth  are  given 
by  substituting  3.75  for  3  in  the  formula. 


GENERAL  METHOD  FOR  JUDGING  WATERED 
AND  SKIMMED  MILK 

Having  found  in  a  sample  of  milk  (i)  the  per  cent, 
of  fat,  (2)  the  specific  gravity  of  the  milk  and  (3)  of 
the  milk-solids,  (4)  the  per  cent,  of  solids,  and  (5)  of 
solids-not-fat,  one  may  arrive  at  fairly  safe  conclu- 
sions in  regard  to  the  watering  and  skimming  by 
making  comparison  with  the  percentages  of  constitu- 
ents present  in  average  normal  milk.  In  forming  such 
conclusions,  the  following  facts  should  be  kept  in 
mind: 

1.  Water  has  a  lower  specific  gravity  than  milk. 

2.  Watering  milk  decreases  (a)  the  lactometer  read- 
ing, (b)  the  fat,  (c)  total  solids,  and  (d)  solids-not-fat. 

3.  Water  has  a  higher  specific  gravity  than  milk-fat. 


2O6  MODERN    METHODS  OF   TESTING   MILK 

4.  Skimming  milk  (a)  increases  the  lactometer  read- 
ing, (b)  decreases  the  fat  and  total  solids,  (c)  slightly 
increases  the  solids-not-fat,  and  (d)  increases  the  spe- 
cific gravity  of  the  milk-solids. 

5.  Skimming  and  watering  decrease  all  constituents, 
but  lower  the  fat  more  in  proportion  than  the  solids 
and  solids-not-fat. 

6.  Skimming  and  watering  may  produce  the  same 
specific  gravity  as  in  normal  milk. 

7.  The  amount  of  fat  in  milk  is  more  variable  than 
the  amount  of  solids-not-fat. 

8.  Herd  milk  which  shows  a  lactometer   reading 
above  33.5,  along  with  a  low  percentage  of  fat,  and  a 
specific  gravity  of  solids  above  1.40,  can  be  regarded 
as  skimmed. 

9.  Herd  milk  showing  a  lactometer  reading  below 
28  may  be  regarded  as  watered,  especially  with  low 
fat,  solids  and  solids-not-fat. 

Milk  is  watered  when  (i)  the  specific  gravity  of 
the  milk  is  low,  (2)  the  percentage  of  fat  and  solids- 
not-fat  is  low  and  (3)  the  specific  gravity  of  the  milk- 
solids  is  between  1.25  and  1.35.  - 

Milk  is  skimmed  when  (i)  the  specific  gravity  of 
the  milk  and  of  the  milk-solids  is  high;  when  (2) 
the  per  cent,  of  solids-not-fat  is  high,  and  when  (3) 
the  per  cent,  of  fat  and  solids  is  low. 

Milk  is  watered  and  skimmed  when  (i)  the  spe- 
cific gravity  of  the  milk  is  normal  or  otherwise,  (2) 
the  specific  gravity  of  the  milk-solids  is  normal  or  high, 
and  (3)  the  per  cent,  of  fat  and  solids-not-fat  is  low, 


TESTING   MILK   FOR   ADULTERATIONS  2OJ 

DETECTION  OF  FOREIGN  SUBSTANCES  IN  MILK 

The  foreign  substances  most  frequently  found  in 
milk  are  preservatives  and  coloring  matters.  The  pre- 
servatives in  common  use  are  formalin,  boric  acid, 
borax  and  sodium  bicarbonate.  The  coloring  matters 
generally  used  are  annatto  and  coal-tar  dyes  (azo- 
colors),  which  are  added  to  milk  to  make  it  look  rich, 
and,  especially  in  case  of  skimmed  and  watered  milk, 
to  cover  up  the  signs  of  such  adulterations. 

Test  for  annatto. — To  10  cc.  of  milk  in  a  test-tube 
add  10  cc.  of  ether,  shake  vigorously  and  let  stand  un- 
til the  ether  separates  on  top  of  the  milk.  If  annatto 
is  present,  the  layer  of  ether  will  be  yellow,  the  depth 
of  color  depending  on  the  amount  of  annatto  present. 

Test  for  Coal-Tar  Dyes. — The  azo-colors,  which 
are  the  ones  most  commonly  used  in  coloring  milk,  may 
be  detected  by  adding  10  cc.  of  milk  to  10  cc.  of  strong 
hydrochloric  acid  and  mixing,  when  a  pink  coloration 
appears. 

Tests  for  Formalin. — Formalin,  which  is  a  40 
per  cent,  solution  of  formaldehyde,  is  commonly  di- 
luted and  sold  under  such  names  as  "Freezine,"  "Ice- 
line,"  etc.,  which  contain  from  2  to  6  per  cent,  of  for- 
maldehyde. In  making  the  Babcock  test  in  milk,  the 
presence  of  formalin  may  be  shown  when  a  marked 
violet  layer  forms  at  the  junction  of  the  acid  and  milk 
just  after  pouring  the  acid  into  the  test-bottle.  The  test 
may  also  be  performed  by  taking  10  cc.  of  milk  in  a 
test-tube  or  Babcock  test-bottle,  adding  dilute  ferric 
chloride  and  5  cc.  of  sulphuric  acid,  such  as  is  used  in 
the  Babcock  test,  pouring  the  acid  down  the  side  of  the 
tube  so  that  it  does  not  mix  with  the  milk. 


2O8  MODERN    METHODS  OF   TESTING   MILK 

Leach's  test,  which  is  more  delicate,  is  performed 
as  follows:  Make  a  solution  of  hydrochloric  acid  (spe- 
cific gravity  1.2)  containing  2  cc.  of  10  per  cent,  ferric 
chloride  per  liter.  Add  10  cc.  of  this  solution  to  10 
cc.  of  milk  in  a  white  teacup  and  heat  slowly  over  a 
flame  to  boiling,  giving  the  cup  a  rotary  motion.  If 
formalin  is  present,  a  violet  coloration  appears,  vary- 
ing in  depth  with  the  amount  present. 

Test  for  borax  and  boric  acid. — 'To  25  cc.  of  milk 
add  lime  water,  until  the  milk  is  alkaline,  evaporate  to 
dryness  and  burn  to  an  ash  in  a  small  porcelain  or 
platinum  dish.  To  the  ash  add  a  few  drops  of  dilute 
hydrochloric  acid,  not  too  much ;  then  add  a  few  drops 
of  water  and  place  in  this  water  solution  a  strip  of 
turmeric-paper  (obtainable  at  drug-stores).  Then  dry 
the  paper,  when  a  cherry-red  color  will  appear  on  the 
paper  if  either  borax  or  boric  acid  is  present.  This  test 
is  made  still  more  certain  by  moistening  the  reddened 
paper  with  a  drop  of  an  alkali  solution,  when  the  pa- 
per turns  to  a  dark-olive  color  in  the  presence  of  borax 
or  boric  acid. 

Test  for  sodium  carbonate. — To  10  cc.  of  milk  add 
10  cc.  of  alcohol  and  a  few  drops  of  a  i  per  cent,  so- 
lution of  rosolic  acid.  Carbonates  are  present  if  a 
rose-red  color  appears,  while  pure  milk  shows  a  brown- 
ish-yellow color. 

ADULTERATIONS  OF  CREAM 

The  adulterants  of  cream  are  the  same  as  those  for 
milk  and  are  detected  in  the  same  manner.  Gelatine 
and  sucrate  of  lime  are  used  to  some  extent  to  give 
cream  a  greater  consistency. 


TESTING  MILK  FOR  ADULTERATIONS 


209 


ADULTERATIONS  OF  BUTTER 

The  most  common  adulteration  of  butter  is  substi- 
tution, in  part  or  in  whole,  of  fat  other  than  butter- 
fat,  such  as  products  from  beef-fat  and  lard.  Occa- 
sionally preservatives  are  found,  such  as  occur  in  milk. 
"Renovated"  or  "process"  butter  is  made  from  refuse 
butter  that  can  not  be  disposed  of  otherwise  on  the 
market.  Excessive  water  or  casein  should  be  regarded 
as  an  adulteration.  Harmless  coloring  matter  has  been 
universally  allowed.  The  absolute  identification  of 
such  adulterants  as  oleomargarin  requires  somewhat 
elaborate  chemical  methods.  Only  simple  tests  can 
be  given  here. 

Foam-test  for  oleomargarin  and  "renovated"  but- 
ter.— Melt  in  an  ordinary  tablespoon  a  piece  of  the 
suspected  butter  about  the  size  of  a  small  chestnut, 
holding  it  over  a  small  flame, — a  candle  flame  will  do. 
Stir  the  fat,  while  melting,  with  a  match  or  similar 
stirrer.  Then  lower  the  spoon  into  the  flame  and  let 
the  fat  boil  vigorously,  stirring  thoroughly  several 
times  during  the  boiling  and  not  neglecting  the  outer 
edges.  Oleomargarin  and  "renovated"  butter  boil 
with  marked  noise,  sputtering  more  or  less  and  pro- 
ducing little  or  no  foam.  Genuine  butter  generally 
boils  with  much  less  noise  and  foams  up  vigorously. 

Milk-Test  for  oleomargarin. — In  a  tin  measuring- 
cup  take  about  one  gill  of  sweet  milk  or  water,  heat 
to  about  140°  F.  and  then  add  a  slightly  rounded  tea- 
spoonful  of  the  suspected  sample.  Stir  with  a  small 
piece  of  wood,  about  the  size  of  a  match  or  smaller, 
until  the  fat  is  melted.  Then  immerse  the  cup  to  about 
one-third  of  its  height  in  a  pan  of  water  in  which  there 


2IO  MODERN    METHODS   OF  TESTING   MILK 

are  several  large  pieces  of  ice.  Stir  the  liquid  contin- 
uously, alternating  a  circular  and  crosswise  motion, 
until  the  fat  hardens,  when  it  can  be  easily  collected 
into  one  lump  by  means  of  the  wooden  stirrer,  if  it  is 
oleomargarin ;  but,  if  butter,  the  fat  will  form  little 
granules  and  can  not  be  collected  in  one  lump.  When 
milk  is  used  in  the  test,  it  should  contain  as  little  fat 
as  possible.  In  this  test  "renovated"  butter  behaves 
like  genuine  butter. 

ADULTERATIONS  OF  CHEESE 

Only  two  kinds  of  adulteration *  are  common  in 
American  cheddar  cheese:  (i)  The  removal  of  fat  in 
varying  degrees  producing  so-called  skim-cheese,  and 
(2)  the  use  of  fat  other  than  milk- fat,  producing  the 
so-called  filled  cheese.  Harmless  coloring  matter  is 
allowed.  Cheese  containing  less  than  32  per  cent,  of 
fat  can  be  regarded  as  having  been  made  from  milk 
containing  less  than  its  normal  amount  of  fat.  The 
per  cent,  of  fat  in  filled  cheese  is  generally  lower  than 
in  cheese  made  from  normal  milk. 


CHAPTER  XVI 
The  Babcock  Test  Applied  to  Farm  Conditions 

I 

The  Babcock  test  finds  application  on  the  farm  of 
every  dairyman  in  one  or  more  of  the  following  ways : 

i)  In  testing  the  quality  of  milk  in  respect  to  fat 
produced  by  individual  cows  and  by  the  herd. 

(2)  In  testing  cream. 

(3)  In  testing  skim-milk. 

(4)  In  testing  buttermilk. 

(5)  In  testing  milk  and  cream  as  a  means  of  self- 
protection. 

TESTING  COWS 

The  most  effective  test  of  the  value  of  a  dairy  cow 
is  the  production  of  milk  and  of  milk-fat.  Evidence 
has  been  carefully  collected  showing  that  many  cows 
in  this  country  are  kept  at  an  actual  loss.  The 
owners  of  such  cows  may  be  conscious  of  the  fact 
that  they  are  not  prospering,  but  without  having  any 
idea  of  the  cause.  The  amount  of  fat  in  milk  required 
for  various  purposes  differs  somewhat.  For  ordi- 
nary market  purposes,  where  consumers  take  as  a 
matter  of  course  any  kind  of  milk  delivered  to  them, 
the  most  profitable  cow  is  the  one  producing  a  large 
yield  of  milk,  which  generally  means  a  low  percentage 
of  fat,  frequently  just  enough  to  keep  above  the  legal 
standard.  The  statement  applies  to  milk  sold  by  bulk 

211 


212  MODERN    METHODS  OF  TESTING   MILK 

or  by  weight  alone,  whether  sold  for  direct  consump- 
tion or  taken  to  a  cheese-factory  or  creamery.  But 
whenever  milk  is  paid  for  according  to  its  percentage 
of  fat,  as  in  certain  forms  of  market  milk,  at  cream- 
eries, at  condenseries,  and  at  progressive  cheese-fac- 
tories, the  cow  producing  the  largest  amount  of  milk- 
fat  will  nearly  always  be  found  the  most  profitable. 
As  a  rule,  a  pound  of  milk-fat  can  be  produced  at  less 
cost  in  rich  milk  than  in  poor  milk.  The  only  method 
of  ascertaining  accurately  the  value  of  a  cow  or  of  a 
herd  for  the  production  of  milk-fat  is  by  testing  the 
milk.  The  real  object  of  a  test  is  to  find  the  total  num- 
ber of  pounds  of  fat  produced  in  the  milk  for  a  defin- 
ite period  of  time,  the  most  satisfactory  unit  being  one 
period  of  lactation,  that  is,  from  the  time  of  calving 
to  the  time  of  becoming  dry. 

In  testing  the  value  of  a  cow  for  the  production  of 
milk- fat,  two  factors  must  be  considered:  (i)  The 
amount  of  milk  produced  and  (2)  the  per  cent,  of  fat 
in  the  milk.  The  first  amount  is  obtained  by  weigh- 
ing the  milk,  and  the  second  by  testing  the  milk  by 
the  Babcock  test.  From  these  data  the  amount  of 
milk-fat  produced  is  easily  found. 

In  applying  the  Babcock  test  on  the  farm  to  indi- 
vidual cows,  certain  details  need  to  be  considered, 
such  as  (i)  the  duration  of  the  testing,  (2)  the  fre- 
quency of  testing,  (3)  the  method  of  sampling,  (4) 
weighing  the  milk,  (5)  keeping  records,  and  (6)  cal- 
culating results.  In  carrying  out  the  work  of  the 
milk-test,  all  necessary  details  are  given  in  Chapter 
IV,  p.  57- 

Duration  of  testing. — For  best  results,  the  tests 


FARM    CONDITIONS  213 

should  be  made  at  intervals  for  a  whole  period  of  lac- 
tation. 

Frequency  of  testing. — It  is  not  practicable  to  test 
the  milk  of  every  milking  for  fat  and  it  is  not  neces- 
sary. On  the  other  hand,  the  testing  of  a  single  milk- 
ing or  of  a  day's  milk  or  even  of  a  week's  milk  is  in- 
sufficient, since,  for  many  reasons,  the  percentage  of 
fat  may  vary  greatly  from  one  time  to  another.  The 
following  plan  combines  a  high  degree  of  accuracy 
with  the  least  amount  of  labor:  Make  the  first  fat- 
test in  about  two  weeks  after  the  cow  calves  and  then 
repeat  it  regularly  once  in  two  weeks  during  the  period 
of  lactation.  Even  a  monthly  testing  will,  however, 
give  fairly  accurate  results. 

Method  of  sampling. — When  a  single  cow's  milk 
is  to  be  tested,  the  following  precautions  should  be 
observed  in  taking  the  sample : 

( i )  The  cow  must  be  milked  dry  at  the  milking  pre- 
vious to  the  one  to  be  tested.  (2)  On  the  day  of  milk- 
ing for  the  test,  the  cow  is  milked  as  completely  as 
possible  each  time.  (3)  After  the  morning's  milk- 
ing, the  milk  is  well  mixed  by  pouring  from  one  pail 
to  another  or  by  stirring  with  a  dipper,  and  about  a 
gill  is  at  once  dipped  out  and  poured  into  a  pint  fruit- 
jar,  which  has  been  thoroughly  cleaned  and  scalded. 
The  sample  is  kept  in  a  cool  place.  Repeat  the  samp- 
ling with  the  evening's  milk  or  with  each  milking,  if 
the  cow  is  milked  more  than  twice  a  day,  adding  a  sam- 
ple of  each  to  the  jar  containing  the  morning's  milk. 
(4)  Make  a  test  before  the  milk  can  sour,  mixing  well 
before  taking  samples  for  the  test  by  pouring  back 
and  forth  a  few  times  from  one  vessel  to  another.  If 


214  MODERN    METHODS   OF   TESTING   MILK 

it  is  impossible  to  make  the  test  promptly,  add  bi- 
chromate of  potash  to  preserve  the  sample,  as  directed 
on  p.  30.  (5)  In  testing  the  milk  of  several  cows  at 
the  same  time,  label  each  sample- jar  with  the  number 
or  name  of  the  cow  furnishing  the  milk.  (6)  If  the 
milk  is  to  be  tested  also  for  solids  by  the  lactometer, 
take  about  a  half -pint  sample  from  each  milking. 

More  strictly  accurate  results  are  secured  if  each 
milking  is  sampled  by  a  tube,  as  stated  on  p.  27. 

Weighing  milk. — In  testing  a  cow,  the  milk  must 
always  be  weighed  on  the  testing  day  immediately  af- 
ter the  milking  is  completed.  As  it  is  so  easy  to  weigh 
milk,  it  is  desirable  to  weigh  the  milk  at  every  milking, 
or,  at  least,  on  two  or  three  days  each  week.  Accurate 
spring  scales  of  moderate  cost  are  available. 

Keeping  records. — Records  of  each  cow  tested 
should  be  carefully  kept,  the  following  facts  being  re- 
corded: (i)  Date,  (2)  name  of  cow,  (3)  pounds  of 
milk  given,  (4)  per  cent,  of  fat  in  milk,  (5)  lactometer 
reading,  if  desired. 

Calculating  results. — The  following  data  can  be  de- 
rived by  calculation  from  the  facts  recorded  above: 
(i)  Pounds  of  fat  produced  on  day  of  test,  (2)  pounds 
of  fat  and  milk  produced  each  month,  (3)  pounds  of 
fat  and  milk  produced  for  one  period  of  lactation. 

The  amount  of  fat  on  the  day  of  the  test  is  found 
by  multiplying  the  total  number  of  pounds  of  milk 
given  by  the  per  cent,  of  fat  found  and  dividing  by 
100.  For  example,  if  the  day's  yield  of  milk  is  25 
pounds  and  the  per  cent,  of  fat  is  4,  the  day's  milk 
contains  i  pound  of  milk- fat.  (See  p.  253). 

The  amount  of  milk  and  fat  produced  each  month 


FARM    CONDITIONS 


215 


is  found  as  follows,  when  the  test  is  made  once  in  two 
weeks :  Add  the  daily  yields  of  milk  for  the  day  of 
the  test  and  for  one  week  before  and  one  week  after 
the  test,  thus  obtaining  the  milk  yield  for  15  days. 
Multiply  this  sum  by  the  per  cent,  of  fat  found  on  the 
day  of  the  test  and  the  result  is  the  fat  yield  for  half 
a  month.  This  added  to  the  next  half  month  gives  the 
yield  of  fat  for  the  month. 

The  monthly  yields  of  milk  and  fat,  added  together 
at  the  end  of  the  period  of  lactation,  give  the  total 
yields  for  the  period. 

APPLICATION  OF  RESULTS  OF  TESTING  INDI- 
VIDUAL COWS 

A  progressive  dairyman  will  discard  from  his  herd 
any  animal  that  can  not  produce,  at  least,  200  pounds 
of  milk-fat  in  a  year,  especially  if  the  milk  is  sold  on 
the  basis  of  its  fat  content ;  and  he  will  aim,  by  means 
of  intelligent  breeding,  feeding  and  care,  to  increase 
the  annual  yield  of  milk-fat  to  250  or  300  pounds  for 
each  cow. 

TESTING  CREAM  ON  THE  FARM 

There  are  several  conditions  under  which  it  is  of 
advantage  to  test  cream  on  the  farm  in  order  to  know 
its  fat  content. 

When  a  dairyman  is  producing  cream  to  sell  directly 
to  consumers,  it  is  important  to  know  its  percentage 
of  fat,  in  order  that  it  may  be  uniform  from  day  to 
day,  whatever  the  desired  percentage  may  be.  The 
work  of  the  cream-separator  may  be  controlled  ac! 


2l6  MODERN    METHODS   OF   TESTING   MILK 

vantageously  only  by  knowing  the  percentage  of  fat 
in  the  cream  produced.  In  states  where  a  certain  per- 
centage of  fat  in  cream  is  required  by  law,  it  is  im- 
portant for  the  dairyman  to  know  that  his  product  is 
up  to  standard  before  he  sells  it. 

In  making  butter  on  the  farm,  better  results  can 
be  secured  by  having  the  cream  of  a  uniform  rich- 
ness in  fat,  and  the  percentage  of  fat  in  cream  can 
be  accurately  known  and  regulated  only  by  testing. 

TESTING  SKIM-MILK  AND  BUTTERMILK  ON 
THE  FARM 

The  completeness  with  which  fat  is  removed  from 
milk  by  different  methods  of  creaming,  whether  by 
separator  or  by  gravity  processes,  can  be  known  accu- 
rately only  by  testing  the  skim-milk  for  its  fat  content. 
With  the  knowledge  furnished  by  testing,  one  is  in 
position  to  prevent  further  losses  when  they  are  known 
to  exist.  Similarly,  the  efficiency  of  churning  may  be 
found  by  testing  the  buttermilk  for  its  fat  content. 

TESTING  MILK  AND   CREAM  FOR  SELF- 
PROTECTION 

When  dairymen  sell  milk  or  cream  to  milk-dealers, 
creameries,  cheese-factories,  shipping-stations,  con- 
denseries,  etc.,  on  the  basis  of  the  per  cent,  of  fat  in 
milk,  it  is  often  a  matter  of  satisfaction  to  know  that 
the  tests  which  serve  as  a  basis  of  payment  are  cor- 
rect. If  a  dairyman  will  take  pains  to  acquire  the  skill 
necessary  to  perform  the  operations  of  the  Babcock 
test,  he  can  satisfy  himself  easily  in  regard  to  the  ac- 


FARM    CONDITIONS 

curacy  of  the  tests  of  his  milk  made  by  others.  In 
cases  where  a  purchaser  reports  the  test  lower  than 
it  is,  his  dishonesty  can  be  detected  by  means  of  home 
testing. 

It  is  also  important  for  the  dairyman  who  sells  milk 
directly  to  consumers  to  know  that  his  milk  is  above 
the  legal  standard.  Much  annoyance  and  expense  may 
sometimes  be  saved  by  knowing  the  percentage  of  fat 
and  solids  in  the  milk  one  sells. 


CHAPTER   XVII 

Methods  of  Commercial  Testing  and  Scoring 
of  Butter  and  Cheese 

In  commercial  transactions  in  butter  and  cheese, 
certain  points  or  qualities  have  been  adopted  as  a  basis 
or  standard  in  judging  the  commercial  value  of  these 
products.  The  terms  used  in  expressing  the  different 
qualities  vary  considerably  in  different  market  cen- 
ters, and  the  same  expression  is  used  with  different 
meanings  by  different  persons.  Frequently  individ- 
uals use  terms  that  are  strictly  local  or  personal.  It 
is  desirable  that  there  should  be  a  uniform  usage  and 
a  common  understanding  in  respect  to  the  terms  used 
in  judging  dairy  products.  The  attempt  is  made  here 
to  discuss  the  terms  in  common  use  and  to  define  them 
as  well  as  may  be,  in  the  hope  that  it  may  serve  as  a 
beginning  in  bringing  about  a  general  agreement  in 
respect  to  the  use  and  understanding  of  the  expres- 
sions employed  in  testing  and  scoring  dairy  products. 
The  definitions  here  given  can  hardly  be  expected  to 
be  in  full  agreement  with  the  usage  of  everyone,  since 
individuals  differ  from  one  another  so  much  in  their 
use  of  these  terms. 

SAMPLING  AND  TESTING  BUTTER 

In  obtaining  a  sample  of  butter  from  a  package  for 
examination,  a  butter-trier  (Fig.  52)  is  used.  This 
is  inserted  its  whole  length,  if  possible,  into  the  but- 

218 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE 

ter,  turned  around  once  and  then  drawn  out,  bringing 
with  it  a  long,  round  plug  as  a  sample.  The  plug,  as 
soon  as  drawn,  is  examined  for  flavor  by  smelling  and 
next  by  tasting.  It  is  then  broken  across 
to  examine  the  grain  or  texture,  and  then 
other  qualities  are  examined  in  turn. 

TERMS  USED  IN  DESCRIBING 
QUALITIES  OF  BUTTER 

The  qualities  that  have  been  selected 
to  serve  as  a  basis  or  standard  in  the 
commercial  testing  and  scoring  of  but- 
ter are  as  follows:  (i)  Flavor,  (2)  tex- 
ture, (3)  body,  (4)  moisture,  (5)  color, 
(6)  salt  and  (7)  appearance. 

Flavor. — By  flavor  is  meant  the  qual- 
ity that  is  perceptible  to  the  senses  of 
smell  and  taste.  The  sense  of  smell  is, 
as  a  rule,  capable  of  being  developed  so 
as  to  be  more  highly  sensitive  than  the 
sense  of  taste  in  detecting  variations  of 
flavor.  The  flavor  in  normal  butter  is 
due  to  the  formation  of  certain  organic 
compounds  in  minute  quantities  during 
the  cream-ripening  process.  What  spe- 

.-  BUTTER  TRIER 

cmc  compounds  these  are  has  not  yet 

been  learned.     The  odor  is  not  that  of  lactic  acid, 

since  that  is  odorless. 

Testing  Flavor. — The  flavor  is  obtained  by  placing 
the  plug  of  butter  under  the  nose  as  soon  as  possible 
after  the  plug  is  drawn.  A  portion  of  the  butter  is 
also  tasted. 


22O  MODERN    METHODS   OF   TESTING   MILK 

Terms  describing  flavors. — The  following  terms 
are  selected  from  the  great  variety  of  names  that  are 
applied  to  various  flavors  found  in  butter:  (i)  Per- 
fect, (2)  quick,  (3)  clean,  (4)  light,  (5)  buttermilk, 
(6)  rancid,  (7)  tallowy,  (8)  cowy,  (9)  fishy,  (10) 
tainted,  (n)  stable,  (12)  weedy,  (13)  cheesy. 

(1)  Perfect  flavor  applies  to  butter  which  possesses 
the  characteristic  aroma  and  taste  of  high-grade  but- 
ter in  a  well-marked  degree.     It  is  difficult  to  de- 
scribe this  flavor  adequately,  but  it  is  commonly  char- 
acterized as  nutty,  clean,  pleasantly  aromatic,  delicate 
and  sweet.     Perhaps  the  best  description  of  it  is  to 
liken  it  to  the  flavor  of  clean,  well-ripened  cream.     It 
should  be  entirely  free  from  rancidity  or  any  unusual 
flavor. 

(2)  Quick  flavor  is  so  delicate  and  volatile  that  it 
disappears  quickly;  "high"  is  also  applied  to  the  same 
condition. 

(3)  Clean  flavor  is  free  from  every  trace  of  unpleas- 
ant aroma  or  taste. 

(4)  Light  or  flat  flavor  in  butter  indicates  absence  of 
marked  flavor,  due  to  lack  of  cream-ripening,  to  ex- 
cessive washing  of  granules  and  to  other  conditions. 

(5)  Buttermilk  flavor  is  somewhat  sour  in  taste  and 
like  buttermilk  in  aroma.    It  is  due  to  the  presence  of 
an  excessive  amount  of  buttermilk  in  the  butter. 

(6)  Rancid  flavor  is  that  of  butyric  acid,  the  pres- 
ence of  which  is  due  to  the  use  of  over-aged  cream  or 
milk  or  to  age  of  butter,  in  which  butyric  acid  fer- 
mentation has  occurred.     When  the  flavor  is  strong, 
it  produces  an  unpleasant,  strangling  or  choking  sen- 
sation in  a  sensitive  throat.     The  odor  is  very  pene- 
trating and  lasting. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  221 

(7)  Tallowy  flavor  is  like  that  of  tallow. 

(8)  Cowy  flavor  refers  to  the  animal  odor,  particu- 
larly as  noticed  in  the  breath  of  a  cow.    It  appears  to 
be  especially  prominent  in  cows  freshly  turned  into 
pasture. 

(9)  Fishy  odor  is  rather  suggestive  of  salted  cod- 
fish.   It  is  usually  due  to  a  special  form  of  fermentation 
appearing  in  the  milk  and  cream. 

(10)  Tainted  flavor  covers  a  variety  of  odors  and 
tastes  that  are  offensive  in  varying  degrees. 

(n)  Stable  flavor  is  the  one  characteristic  of  cow 
manure. 

(12)  Weedy  flavor  includes  such  abnormal  flavors  as 
may  come  from  onions,  leeks,  cabbages,  turnips,  etc. 

(13)  Cheesy  flavor  suggests  the  flavor  of  cheese  and 
is  due  to  fermentation  changes  in  the  proteid  of  but- 
ter; it  is  more  common  in  unsalted  butter. 

Texture. — The  texture  of  butter  refers  to  what  is 
called  the  grain  and  depends  upon  the  condition  of  the 
butter-granules.  In  its  first  formation  in  churning, 
butter  appears  in  very  small,  irregular  grains  or  gran- 
ules. These  grains  retain  their  individuality  in  large 
measure  throughout  the  rest  of  the  process  of  butter- 
making  and  even  in  the  finished  product.  The  more 
distinct  the  individuality  of  the  granules  can  be  kept 
in  making  the  butter  into  a  solid  mass,  the  better  is 
the  texture. 

Testing  texture. — The  granular  texture  of  butter 
is  seen  when  a  plug  or  chunk  of  butter  is  broken  into 
parts  transversely,  giving  somewhat  the  fractured  ap- 
pearance seen  in  broken  steel  and  free  from  a  smooth, 
greasy  appearance.  Another  method  of  testing  tex- 


222  MODERN    METHODS   OF   TESTING   MILK 

ture  is  to  pass  a  knife-blade  or  butter-trier  through 
the  butter;  when  it  is  withdrawn,  the  trier  is  clean 
and  free  from  any  greasy  appearance,  if  the  texture 
is  good. 

Terms  describing  texture. — The  terms  used  to  de- 
scribe texture  are  (i)  perfect,  (2)  poor  grain,  and 
(3)  salvy. 

(1)  Perfect  texture  in  butter  is  shown  by  the  gran- 
ular formation,  as  described  above. 

(2)  Poor  grain  texture  in  butter  is  shown  by  less 
marked  grain  and  a  more  or  less  smooth,  greasy  ap- 
pearance on  the  broken  surfaces. 

(3)  Salvy  texture  applies  to  butter  in  which  the 
grain  is  more  or  less  destroyed  and  the  smooth,  greasy 
appearance  of  the  broken  surface  is  very  marked. 

Defective  texture  in  butter  is  caused  by  allowing 
the  butter-granules  in  the  churn  to  become  too  large 
and  by  working  too  much  or  at  too  high  a  tempera- 
ture. The  granular  texture  of  butter  is  completely  de- 
stroyed by  warming  butter  to  near  its  melting  point. 

Body. — By  this  term  is  meant  the  quality  of  consis- 
tency, firmness  or  hardness,  as  shown  by  not  melting 
or  softening  too  easily. 

Testing  body. — The  body  of  a  sample  of  butter  can 
be  ascertained  by  pressing  a  portion  of  the  plug  be- 
tween the  thumb  and  fingers,  and  also  by  pressing  be- 
tween the  tongue  and  roof  of  the  mouth. 

Terms  describing  body. — The  terms  used  to  de- 
scribe the  body  of  butter  are:  (i)  perfect,  firm  or 
solid,  (2)  hard  or  tallowy,  (3)  weak-bodied,  (4) 
sticky. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  223 

(1)  Perfect  body  in  butter  is  shown  by  firmness  or 
solidity  under  proper  conditions  of  temperature.  When 
pressed  between  the  fingers  or  on  the  tongue  it  shows 
a  certain  amount  of  resistance. 

(2)  Hard  or  tallowy  body  is  shown  by  excessive  so- 
lidity, being  characteristic  of {  butter  made  from  cows 
far  along  in  lactation,  or  in  the  case  of  cows  heavily 
fed  on  cotton-seed  meal. 

(3)  Weak-bodied  butter  is  lacking  in  firmness,  more 
or  less  soft,  melting  more  easily  on  warming  than  a 
perfect-bodied  butter.     Weak-bodied  butters  are  usu- 
ally salvy  in  texture  and  high  in  moisture.     Certain 
feeds,  such  as  gluten  meal,  tend  to  increase  the  soft- 
ness of  butter. 

(4)  Sticky  body  in  butter  is  shown  by  extreme  soft- 
ness amounting  to  stickiness. 

Moisture. — The  water  in  butter  should  be  so  thor- 
oughly incorporated  with  the  fat  that  it  does  not  appear 
in  the  form  of  free  beads  of  water  visible  to  the  eye. 
Water  should  not  run  off  the  trier  when  a  sample  is 
drawn.  The  water  should  also  be  clear  and  trans- 
parent. 

Testing  moisture. — The  sample  of  butter  is  exam- 
ined for  the  appearance  of  moisture  or  brine  in  respect 
to  the  completeness  of  its  incorporation  and  its  clear- 
ness. 

Terms  describing  moisture. — The  following  terms 
are  used  to  describe  the  condition  of  moisture  in  but- 
ter: (i)  Perfect,  (2)  excessive,  (3)  milky  or  turbid. 

(1)  Perfect  moisture  in  butter  is  shown  by  the  ab- 
sence of  any  visible  moisture  in  the  form  of  drops. 

(2)  Excessive  moisture  is  shown  by  the  presence  of 


224  MODERN    METHODS  'OF   TESTING   MILK 

water  easily  apparent  to  the  eye.  Butter  may  some- 
times contain  so  much  water  as  to  be  called  "mushy." 

(3)  Milky  or  turbid  moisture  or  brine  appears  more 
or  less  milky,  being  due  to  the  presence  of  too  much 
buttermilk. 

Relation  of  texture,  body  and  moisture. — Considera- 
ble confusion  prevails  in  the  use  of  the  terms  texture, 
body  and  moisture.  Some  use  the  term  texture  to  in- 
clude also  body  and  moisture;  others  use  the  term 
body  to  include  texture,  while  others  use  the  expres- 
sion "body  and  grain"  to  cover  all  three  qualities.  Tex- 
ture and  body  and  moisture  may  be  influenced  by  the 
same  conditions  and  may  be,  to  some  extent,  interde- 
pendent, but  in  reality  they  are  distinct  properties  and, 
if  they  were  treated  as  such,  needless  confusion  would 
be  avoided. 

Color. — The  color  of  butter  varies  in  different  mar* 
kets  according  to  requirements,  but  most  of  the  but- 
ter made  in  the  United  States  has,  as  its  standard,  an 
even,  bright,  straw-yellow.  Most  butter  in  commerce 
is  colored  artificially,  so  as  to  maintain  a  uniform  ap- 
pearance at  all  seasons  of  the  year.  Somewhat  dif- 
ferent shades  of  color  are  demanded  by  different  mar- 
kets. 

Testing  color. — The  quality  of  color  is  tested 
simply  by  inspection  with  the  eye.  The  thumb-nail  is 
run  along  the  surface  of  the  plug  near  the  edge  of  the 
trier,  and  the  fresh  surface  thus  made  is  examined. 
The  examiner  carries  in  his  mind  the  shade  of  what 
he  regards  as  an  ideal  color  and  judges  the  sample 
under  examination  by  its  comparison  with  his  ideal. 
It  would  lead  to  easier  methods  of  comparison  and 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  225 

more  uniform  results  if  there  could  be  agreed  upon 
a  certain  shade  of  color  which  should  serve  as  a  na- 
tional standard  as  far  as  possible.  Such  a  color  stand- 
ard could  be  furnished  butter-makers  and  examiners- 
of  butter.  Along  with  such  a  standard  color,  there 
could  be  prepared  a  scale  of  shades  which  could  serve 
as  a  basis  for  scoring  color,  i 

Terms  describing  color. — The  terms  used  in  de- 
scribing the  color  of  butter  are:  (i)  perfect,  (2)  light, 
(3)  high,  (4)  reddish,  (5)  mottled,  and  (6)  white- 
specked. 

1 i )  Perfect  color  in  butter  is  a  straw-yellow,  bright, 
and  uniform  throughout  the  mass.     A  plug  of  butter 
held  between  the  light  and  the  eye  should  be  evenly 
translucent  and  not  opaque  or  cloudy. 

(2)  Light  color  is  shown  by  insufficient  color,  the 
yellow  being  too  pale. 

(3)  High  color  is  deeper  yellow  than  called  for  by 
perfect  color. 

(4)  Reddish  color  is  self-explanatory  and  is  due  to 
excessive  use  of  coloring  material. 

(5)  Mottled  color  in  butter  is  shown  by  the  appear- 
ance of  light-colored  portions,  which  may  be  in  spots 
or  streaks  or  waves.    The  term  wavy  is  often  used  to 
indicate  a  variation  of  color  that  is  just  perceptible. 
They  are  not  seen  as  readily  on  a  sample  plug  drawn 
by  a  trier  as  they  can  be  by  cutting  a  lump  of  butter 
across  so  as  to  show  a  smooth,  broad  surface.    Slight 
mottling  is  apt  to  escape  observation  when  the  exam- 
ination is  made  only  of  a  plug.     Mottling  is  due  to 
the  action  of  salt  upon  buttermilk  retained  in  the  but- 
ter.    The  light  portions  owe  their  color  to  the  pres- 


226  MODERN    METHODS   OF   TESTING    MILK 

ence  of  the  casein  lactate  of  buttermilk.  Removal  of 
buttermilk  from  the  butter-granules  prevents  mottling. 
(Bulletin  No.  263,  N.  Y.  Agr.  Exp.  Sta.  1905). 

(6)  White-specked  color  in  butter  appears  in  white 
specks  of  varying  size,  but  usually  small.  They  are 
due  to  particles  of  coagulated  casein  lactate  produced 
in  cream  by  over-ripening,  and  also  to  dried  cream 
particles,  caused  by  lack  of  stirring  during  the  process 
of  ripening. 

Salt. — The  amount  of  salt  in  butter  varies  with  dif- 
ferent markets;  but,  whatever  the  amount  used,  it 
should  be  completely  dissolved  and  evenly  distributed 
through  the  mass  of  butter. 

Testing  butter  for  salt. — The  quality  of  butter  as 
affected  by  salt  is  examined  by  tasting,  sight  and  feel- 
ing. Undissolved  particles  of  salt,  when  they  can  not 
be  felt  on  the  tongue  or  seen,  can  be  detected  by  rub- 
bing some  of  the  butter  between  the  ringers. 

Terms  describing  salt. — The  terms  used  in  de- 
scribing the  quality  of  butter  in  relation  to  salt  are  the 
following:  (i)  Perfect,  (2)  too  salty,  (3)  flat,  (4) 
gritty,  (5)  uneven. 

(1)  Perfect  quality  in  respect  to  salt  in  butter  is 
shown  as  follows :    The  salt  must  be  in  the  proportion 
demanded  by  the  market ;  it  must  be  entirely  dissolved 
and  evenly  distributed. 

(2)  Too  salty  butter  contains  more  salt  than  the 
market  demands. 

(3)  Flat  butter  is  lacking  in  salt  for  the  market  re- 
quirements. 

(4)  Gritty  butter  contains  undissolved  salt. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  227 

(5)  Uneven  salt  in  butter  is  lack  of  uniformity,  some 
portions  of  butter  being  more  salty  than  others. 

Appearance. — Under  this  head  are  included  the 
manner  of  packing,  the  attractive  appearance  of  the 
package,  cleanliness,  etc. 

Testing  appearance. — When  the  cover  of  the  pack- 
age is  removed  for  sampling  the  butter,  the  appearance 
of  the  surface  of  the  butter  is  noticed.  The  outside  of 
the  package  is  also  examined.  The  two  general  quali- 
ties that  must  be  kept  in  mind  in  this  connection  are 
cleanliness  and  neatness. 

Terms  describing  appearance. — The  quality  of  ap- 
pearance of  butter  may  be  considered  under  two  heads, 
(i)  finish  and  (2)  package. 

1 i )  Finish  in  appearance,  in  connection  with  exam- 
ining butter,  refers  to  the  manner  of  packing.     The 
finish  is  perfect  when  the  package  is  lined  with  paraf- 
fin or  with  a  good  quality  of  parchment  paper,  neatly 
placed,  and  the  package  well  filled,  the  surface  being 
even  and  bright.     The  package  should  be  just  evenly 
full.     The  top  should  be  neatly  covered  with  cheese- 
cloth saturated  with  brine. 

(2)  Package. — The  package  is  regarded  as  perfect 
when  of  good  material,  well-made,  clean,  and  neat  in 
appearance.     In  the  same  lot  of  butter  the  packages 
should  all  be  alike  in  size  and  shape. 

SCORING  BUTTER 

The  different  qualities  indicated  above  are  used  in 
a  specific  manner  for  judging  and  fixing  the  com- 
mercial value  of  butter. 


228  MODERN    METHODS   OF   TESTING   MILK 

Scale  of  points. — To  each  quality  is  assigned  a  defi- 
nite numerical  value  and  these  numbers  are  called  a 
scale  of  points.  The  following  scale  of  points  is  in 
common  use  in  many  markets  of  this  country,  the  num- 
bers indicating  perfect  quality  in  each  case,  and  the 
totals  aggregating  100: 

Flavor,  45  points.  Color,  15  points. 

Texture,  (10)    )  Salt,  10  points. 

Body,   (10)         j-25  points.  Appearance,  5  points. 

Moisture,  (5)    )  Total,          100  points. 

Method  of  scoring. — In  scoring  a  sample  of  but- 
ter, an  examination  is  made  with  reference  to  each  of 
the  qualities  mentioned.  In  those  qualities  in  which  it 
is  perfect,  it  is  given  the  values  or  points  assigned 
above.  If  the  butter  is  defective  in  any  quality,  that  is, 
short  of  perfect,  then  a  smaller  value  is  given  than  the 
one  indicated  above  in  the  scale  of  points ;  the  more  de- 
fective the  butter  is  in  any  quality,  the  lower  is  the 
value  or  number  of  points  given  it.  When  all  the 
qualities  have  been  scored,  the  numbers  of  points  as- 
signed to  them  are  added  and  the  total  is  the  score  of 
the  butter  under  examination. 

It  can  readily  be  seen  that  judgment,  trained  by  ex- 
perience, is  required  to  assign  to  each  quality  its  proper 
number  of  points.  The  sense  of  smell  and  of  taste 
must  be  highly  developed  by  training  in  the  field  of 
experience.  The  eye  and  touch  must  also  be  trained 
by  special  experience. 

Score-cards. — For  convenience,  score-cards  are  used 
in  keeping  records  of  the  results  of  scoring  where  many 
samples  are  examined.  The  following  form  illustrates 
a  commercial  score-card: 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  229 

NAME  OR  NUMBER  IDENTIFYING  SAMPLE 

DATE JUDGE 


QUALITY 

SCORE-POINTS 

Sample 
1 

Sample 
2 

Sample 
3 

Sample 
4 

45 

45 

40 

36 

32 

Texture  

10 

8 

10 

8 

7 

Body  

10 

10 

8 

8 

7 

Moisture  

5 

5 

3 

4 

4 

Color  

15 

13 

14 

13 

12 

Salt  

10 

10 

10 

10 

8 

Appearance  

5 

4 

5 

4 

5 

95 

90 

83 

75 

These  scores,  under  the  system  of  grading  described 
below,  would  be  graded  as  follows:  Sample  I,  "ex- 
tras;" sample  2,  "firsts;"  sample  3,  "seconds;"  and 
sample  4,  "thirds." 

In  commerical  scoring,  reasons  for  the  number  of 
points  given  are  not  stated;  but  in  dairy  schools  and 
competitive  public  exhibitions,  where  educational  pur- 
poses are  in  view,  the  reason  for  each  score  should  be 
given.  The  following  form  of  score-card  for  such 
purposes  is  a  suggestion,  which  may  be  modified  to 
suit  any  special  conditions: 

Butter-Scoring — Numerical   and    Descriptive   Card 

Date Judge 

Name  or  number  identifying  butter 


230 


MODERN    METHODS   OF   TESTING   MILK 


NUMERICAL  SCORE. 

Perfection—Flavor,    Texture,   Body,   Moisture,  Color,  Salt.   Appearance 
(45)  (10)  (10)  (5)  (15)        (10)  (5) 

Score  given       —  —          —  — 

DESCRIPTIVE  SCORE   (check  defects  below). 


Flavor 

Texture 

Body 

Moisture 

Color 

Salt 

Appear- 
ance 

Perfect    Quick 

Perfect 

Perfect 

Perfect 

Perfect 

Perfect 

Finish 

Clean     I,ight 

Buttermilk 
Rancid 

Tallowy 
Cowy 

Poot- 
grain 

Salvy 

Firm 
Hard 

Weak- 
bodied 

Exces- 
sive 

Milky 

Light 
High 
Reddish 

Too  salty 
Flat 
Gritty 

Package 

Fishy  Tainted 

Sticky 

Mottled 

Uneven 

Stable  Weedy 
Cheesy 

Wavy 
Specks 

CLASSES  AND  GRADES  OF  BUTTER 

The  following  system  for  classifying  and  grading 
butter  is  taken  from  the  regulations  of  the  New  York 
Mercantile  Exchange: 
Classification : — 

1.  Creamery  Butter  includes  butter  made  in  a  cream- 
ery from  cream  obtained  by  the  separator  system,  or 
from  gathered  cream. 

2.  Imitation     Creamery     Butter     includes     batter 
churned  by  the  dairyman,  collected  in  its  unsalted,  un- 
worked  condition,  and  worked,  salted  and  packed  by 
the  dealer  or  shipper. 

3.  Dairy  Butter  includes  such  as  is  made,  salted 
and  packed  by  the  dairyman  and  offered  in  its  orig- 
inal package. 

4.  Factory  Butter  is  butter  collected  in  rolls,  lumps, 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE   23! 

or  in  whole  packages,  and  reworked  by  the  dealer  or 
shipper. 

5.  Renovated  Butter  is  that  made  by  taking  pure 
butter  and  melting  the  same  and  rechurning  with  fresh 
milk,   cream  or  skim-milk,  or  other  equivalent  pro- 
cess. 

6.  Grease  consists   of  all  grades   of  butter  below 
Fourths  free  from  adulteration. 

7.  Known  Marks  is  a  term  used  to  include  such 
butter  as  is  known  to  the  trade  under  some  particular 
mark  or  designation  and  must  grade  as  Extras,  if 
creamery,  and  as   Firsts,  if  reworked  butter,  in  the 
season  in  which  it  is  offered,  unless  otherwise  speci- 
fied. 

Grades: — Grades  of  butter  must  conform  to  all 
the  following  requirements  and  are  not  determined  by 
score  alone. 

1.  Extras  must  be  of  the  highest  grades  of  butter 
made  in  the  season  when  offered  under  the  different 
classifications ;  90  per  cent,  shall  be  up  to  the  following 
standard  and  the  balance  must  not  grade  below  Firsts : 

(i)Flavor  must  be  fine,  sweet,  clean  and  fresh,  if 
of  current  make ;  and  fine,  sweet  and  clean,  if  held. 
(2)  Body  must  be  firm,  smooth  and  uniform.  (3) 
Color  should  be  a  light  straw  shade,  even  and  uniform. 
(4)  Salt  should  be  medium.  (5)  Package  should  be 
good,  uniform  and  clean.  (6)  Score  must  average  93 
points  or  higher. 

2.  Firsts  is  a  grade  just  below  Extras  and  must 
be  fine  butter  for  the  season  when  made  and  offered, 
under  the  different  classifications,  and  up  to  the  fol- 
lowing standard: 


232  MODERN    METHODS  OF  TESTING   MILK 

(i)  Flavor  must  be  good,  sweet,  clean  and  fresh, 
if  of  current  make ;  and  good,  sweet  and  clean,  if  held. 
(2)  Body  must  be  good  and  uniform.  (3)  Color  must 
be  reasonably  uniform,  neither  too  high  nor  too  light. 

(4)  Salt  should  be  medium.  (5)  Packages  should  be 
good  and  uniform.  (6)  Score  must  average  87  points 
or  higher. 

3.  Seconds  is  a  grade  just  below  Firsts  and  must 
be  good  for  the  season  when  offered  under  the  differ- 
ent classifications,  and  up  to  the  following  standard: 

(i)  Flavor  must  be  reasonably  good  and  sweet.  (2) 
Body,  if  creamery  or  dairy,  must  be  solid-boring.  If 
factory  or  renovated,  must  be  90  per  cent,  solid-bor- 
ing. (3)  Color  must  be  fairly  uniform.  (4)  Salt  may 
be  high,  medium  or  light.  (5)  Package  should  be 
good  and  uniform.  (6)  Score  must  average  80  points 
or  higher. 

4.  Thirds  is  a  grade  just  below  Seconds. 

( i )  Flavor  must  be  reasonably  good ;  may  be  strong 
on  top  and  sides.  (2)  Body  should  be  fair-boring,  if 
creamery  or  dairy,  and  at  least  50  per  cent,  boring  a 
full  trier,  if  factory  or  renovated.  (3)  Color  may  be 
irregular.  (4)  Salt  may  be  high,  light  or  irregular. 

(5)  Packages  should  be   fairly  uniform.    (6)    Score 
must  average  75  points  or  higher. 

5.  Fourths  is  a  grade  just  below  Thirds  and  may 
consist  of  promiscuous  lots. 

( i )  Flavor  may  be  off  and  strong  on  tops  and  sides. 
(2)  Body  is  not  required  to  draw  a  full  trier.  (3) 
Color  may  be  irregular.  (4)  Salt  may  be  high,  light, 
or  irregular.  (5)  Package  may  be  of  any  kind  men- 
tioned at  time  of  sale. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  233 

SAMPLING  AND  TESTING  CHEESE 

Only  the  ordinary  American  cheese,  usually  made 
by  the  cheddar  system,  is  here  considered.  For  com- 
mercial testing,  cheese  is  sampled  by  a  cheese-trier 
in  much  the  same  manner  as  butter.  The  plug  should 
always  be  drawn  from  the  topt  and  not  from  the  side 
in  order  to  avoid  injuring  the  protective  power  of  the 
bandage.  The  plug  drawn  is  examined  by  smelling, 
feeling,  appearance,  etc.,  in  reference  to  the  various 
qualities  mentioned  below. 

TERMS  USED  IN  DESCRIBING  QUALITIES  OF 
CHEESE 

The  following  qualities  have  been  selected  to  serve 
as  a  basis  in  the  commercial  testing  and  scoring  of 
cheese:  (i)  Flavor,  (2)  texture,  (3)  body,  (4)  color, 
(5)  salt,  and  (6)  appearance. 

Flavor. — By  flavor  is  meant  the  quality  that  is  per- 
ceptible to  the  smell  and  taste.  The  sense  of  smell  is 
depended  upon  in  testing  flavor  in  cheese  much 
more  largely  than  is  the  sense  of  taste,  because,  in  ex- 
amining a  large  number  of  samples  of  cheese  in  suc- 
cession, constant  tasting  soon  dulls  not  only  the  sense 
of  taste  but  also  that  of  smell.  Flavor  in  cheese  is 
due  to  the  formation  of  some  unknown  compound  or 
compounds  during  the  ripening  process. 

Testing  flavor  in  cheese. — The  flavor  is  best  ob- 
tained by  direct  smelling  of  the  plug  as  soon  as  it  is 
drawn  and,  in  addition,  by  crushing  and  warming 
some  of  the  cheese  in  the  hand  and  then  smelling. . 

Terms  used  in  describing  cheese  flavors. — From 
a  great  variety  of  names  applied  to  various  flavors 


234  MODERN   METHODS  OF  TESTING  MILK 

found  in  cheese,  the  following  terms  are  selected  for 
consideration:  (i)  Perfect,  (2)  high  or  quick,  (3) 
clean,  (4)  low  or  flat,  (5)  strong,  (6)  too  much  acid, 
(7)  too  little  acid,  (8)  sour,  (9)  sweet  or  fruity,  (10) 
rancid,  (n)  tallowy,  (12)  tainted,  (13)  stable,  (14) 
weedy,  (15)  bitter,  (16)  cowy. 

(1)  Perfect  flavor  applies  to  cheese  when  it  some- 
what resembles  that  of  first-class  butter  with  an  added 
quality  of  its  own  that  is  characteristic  but  cannot  be 
described   further  than  to   call   it  cheese-like.      It  is 
sometimes  described  as  "nutty."     This  flavor  should 
be  marked,  but  not  strong.     It  should  be  free  from 
all  other  flavors,  particularly  the  more  or  less  offen- 
sive products  of  undesirable  fermentations.    The  taste 
should  be  mild  and  somewhat  lasting,  but  should  not 
be  so  sharp  as  to  "bite"  the  tongue. 

(2)  High  or  quick  flavor  is  a  delicate  flavor  that  dis- 
appears quickly. 

(3)  Clean  flavor  is  free  from  every  trace  of  unpleas- 
ant aroma  or  taste. 

(4)  Low  or  fiat  flavor  applies  to  slight  traces,  or 
absence,  of  flavor;  it  is  insipid. 

(5)  Strong  flavor  is  a  good  flavor  very  pronounced 
but  free  from  everything  offensive ;  it  is  a  good  flavor 
strongly  developed. 

(6)  Too  much  acid  applies  to  flavor  that  smells 
somewhat  sour  but  does  not  taste  sour. 

(7)  Too  little  acid  applies  to  a  mild  flavor,  lacking 
in  character. 

(8)  Sour  flavor  is  characterized  by  a  sour  taste 
when  the  cheese  is  fresh,  owing  to  the  presence  of  too 
much  whey. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE   235 

(9)  Sweet  or  fruity  flavor  is  suggestive  of  artificial 
pineapple  odor  and  is  somewhat  "sickish." 

( 10)  Rancid  flavor  is  that  of  butyric  acid,  more  com- 
mon in  old  cheese  than  in  young.     When  very  strong, 
it  affects  a  delicate  throat  with  a  slight  sensation  of 
choking  or  strangling. 

(n)  Tallowy  flavor  is  like  that  of  tallow. 

(12)  Tainted  flavor   includes   a  variety  of  odors, 
mildly  to  strongly  offensive. 

(13)  Stable  flavor  suggests  the  smell  of  cow- ma- 
nure. 

(14)  Weedy  flavor  applies  to  such  abnormal  flavors 
as  come  from  onions,  leeks,  cabbages,  ragweed,  etc. 

(15)  Bitter  flavor  is  self-descriptive.    It  is  often  due 
to  certain  fermentations  that  develop  when  a  cheese 
is  undersalted. 

(16)  Cowy  flavor  is  suggestive  of  the  breath  of  a 
cow  and  may  develop  in  cheese  from  some  form  of 
fermentation. 

Texture. — Texture,  as  applied  to  cheese,  refers 
chiefly  to  compactness  or  appearance  of  solidity,  and 
has  a  meaning  quite  different  from  what  it  has  when 
used  with  reference  to  butter.  It  is  quite  common  to 
regard  the  "body"  as  a  part  of  the  texture,  but  the 
two  qualities  are  clearly  distinct. 

Testing  texture  in  cheese. — The  texture  of  cheese 
is  tested  by  an  examination  of  the  plug  with  reference 
to  the  presence  of  holes.  The  plug  is  broken  in  two 
and  the  broken  ends  examined  for  the  characteristic 
flinty  appearance. 

Terms  describing  texture. — The  following  terms 
are  among  those  most  commonly  used  in  describing 


236  MODERN    METHODS   OF   TESTING   MILK 

texture:  (i)   Perfect,   (2)   close,   (3)   loose,   (4)   me- 
chanical holes,  (5)  gas  or  pin-holes,  (6)  Swiss  holes. 

(1)  Perfect  texture  in  cheese  is  shown  when  a  plug 
or  a  cut  surface  of  the  inside  of  the  cheese  presents 
to  the  eye  a  solid,  compact,  continuous  appearance, 
free  from  breaks,  holes  and  chunks.     When  a  plug 
is  broken  in  two,  it  should  show  a  flaky  appearance, 
termed  a   "flinty"  break,   resembling  the   surface  of 
broken  flint  or  steel. 

(2)  Close  texture   describes   the  appearance  of  a 
cut  surface  of  cheese  when  free  from  all  kinds  of 
holes. 

(3)  Loose  or  porous ^ texture  is  indicated  by  lack  of 
solid  compactness,  being  more  or  less   full  of  holes, 
which  vary  from  a  few  to  enough  to  make  a  spongy 
appearance. 

(4)  Mechanical  holes  in  cheese  are  irregular,  open 
spaces,   caused  by  the   incomplete   cementing  of  the 
pieces  of  curd  in  the  press. 

(5)  Gas-holes  or  pin-holes  are  small  holes,  produced 
by  gaseous  products  of  fermentation. 

(6)  Swiss  holes  are  fairly  large,  round  holes,  such 
as  are  present  in  Emmenthaler  cheese. 

Body. — This  term,  used  in  connection  with  cheese, 
refers  to  the  consistency,  firmness  or  substance  of 
cheese.  It  is  largely  influenced  by  the  amount  of 
fat  and  moisture  in  cheese. 

Testing  body. — This  quality  is  found  by  pressing  a 
piece  of  cheese  between  the  thumb  and  fingers. 

Terms  describing  body. — The  following  terms  are 
among  those  used  in  describing  the  body  of  cheese: 
(i)  Perfect,  (2)  solid  or  firm,  (3)  smooth,  (4)  silky, 
(5)  waxy,  (6)  pasty  or  salvy,  (7)  stiff,  corky,  or 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE    237 

curdy,  (8)  weak-bodied,  (9)  mealy,  (10)  gritty,  (n) 
watery,   (12)   over-dry. 

1 i )  Perfect  body  in  cheese  is  indicated  when  it  feels 
solid,  firm  and  smooth  in  its  consistency  or  substance. 
It  does  not  crumble  under  pressure.     A  plug  drawn 
from  a  cheese  of  perfect  body  should  be  smooth  in  ap- 
pearance and  not  "fuzzy." 

(2)  Solid  or  firm  body  is  indicated  when  cheese  of- 
fers a  certain  amount  of  resistance  under  pressure, 
somewhat  like  that  shown  by  a  piece  of  fat  pork  or 
cold  butter.     The  term  meaty  is  also  used. 

(3)  Smooth-bodied  cheese,  when  pressed  between 
the  thumb  and  fingers,  feels  smooth  and  velvet-like,  as 
distinct  from  harsh,  gritty  or  mealy. 

(4)  Silky-bodied  cheese  is  smooth  in  feeling  but  not 
over-solid  in  consistency. 

(5)  Waxy-bodied  cheese  is  much  the  same  as  silky 
but  possessing  more  firmness  or  solidity. 

(6)  Pasty  or  salvy  cheese  is  very  soft,  usually  from 
an  excess  of  moisture.     When  pressed,  it  sticks  to  the 
fingers. 

(7)  Stiff,  corky  or  curdy  cheese  is  hard,  tough,  over- 
firm;  it  does  not  crush  down  readily  when  pressed  in 
the  hand. 

(8)  Weak  -bodied   cheese   is   very   soft,   lacking  in 
firmness  but  not  necessarily  sticky  like  pasty  cheese. 

(9)  Mealy  cheese  breaks  down  in  fine  crumbs  when 
pressed. 

(10)  GnV/3/-bodied   cheese   feels   harsh   and  gritty 
under  pressure. 

( 1 1 )  Watery-bodied  cheese  is  excessively  soft,  pasty 
and  sticky. 


238  MODERN    METHODS   OF   TESTING   MILK 

(12)  In  an  over -dry  cheese  the  body  is  very  hard 
or  mealy. 

Color. — The  color  of  cheese  varies  considerably, 
whether  artificially  colored  or  not.  There  appears  to 
be  an  increasing  demand  for  uncolored  cheese.  The 
coloring  varies  from  a  pale  yellow  to  a  reddish  yel- 
low, according  to  the  demands  of  special  markets. 

Testing  color. — The  color  is  tested  by  inspection 
with  the  eye,  the  examiner  noticing  particularly  unev- 
enness  and  any  extreme  condition  of  color. 

Terms  describing  color. — Color  in  cheese  is  de- 
scribed by  the  following  terms:  (i)  Perfect,  (2) 
straight,  (3)  translucent,  (4)  white  specks,  (5)  streak- 
ed, (6)  wavy,  (7)  mottled,  (8)  acid-cut,  (9)  high, 
(10)  light,  (n)  uncolored. 

(1)  Perfect  color  in  cheese  is  indicated  by  evenness 
of  color  throughout  the  mass.     A  plug  held  between 
the  eye  and  light  should  appear  somewhat  translucent. 

(2)  Straight  color  is  an  even,  uniform  color  through 
the  whole  cheese. 

(3)  Translucent  applies  to  color  in  cheese  which 
appears  slightly  translucent  when  the  plug  is  held  be- 
tween the  eye  and  the  light. 

(4)  White  specks  is  a  term  that  describes  itself. 
Such  specks  in  cheese  are  a  defect.    They  may  appear 
in  cheese  cured  at  low  temperature. 

(5)  Streaked  color  indicates  that  there  are  light- 
colored  portions  in  the  form  of  streaks. 

(6)Wavy  color  applies  to  lighter  portions  appear- 
ing in  the  form  of  waves. 

(7)  Mottled  color  shows  in  cheese  in  lighter-colored 
spots  of  fairly  large  size,  more  or  less  irregular. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  239 

(8)  Acid-cut  color  is  shown  in  cheese  when  consid- 
erable portions  of  the  cheese  have  been  made  lighter 
in  color  by  the  presence  of  too  much  acid  (whey). 

(9)  High   color   is   indicated  by   a   reddish   color, 
caused  by  using  too  much  coloring  matter.     How- 
ever, the  question  of  color  is  a  relative  one,  because 
the  demand  in  different  markets  varies  from  uncolored 
to  extremely  high  color. 

(10)  Light  color  is  the  term  usually  used  in  describ- 
ing cheese  that  has  been  made  uniformly  dead  white 
by  the  action  of  too  much  acid  (whey). 

( 1 1 )  Uncolored  cheddar  cheese  is  not  white  but  of 
a  light  amber  shade. 

Salt. — The  amount  of  salt  in  cheese  varies  somewhat 
with  different  markets.  There  is  seldom  experienced 
difficulty  of  uneven  salting  in  cheese,  because  the  salt 
slowly  permeates  the  cheese  in  the  ripening  process. 
Little  variations  usually  occur  in  different  parts  of 
the  same  cheese,  but  are  so  slight  as  to  be  incapable  of 
being  noticed  by  ordinary  methods  of  examination. 

Testing  cheese  for  salt. — The  quality  of  cheese  as 
influenced  by  the  salt  is  found  simply  by  tasting. 

Terms  used  in  describing  salt. — In  describing  the 
relation  of  salt  to  cheese,  the  following  terms  are  used : 
(i)  Perfect,  (2)  too  much,  (3)  too  little. 

(1)  Perfect   applies   to    salt   in   cheese    when    just 
enough  has  been  used  to  impart  a  sufficient  taste  of 
salt. 

(2)  Too  much  salt  is  indicated  by  salty  taste.    Too 
much  salt  in  cheese  causes  a  dry,  mealy  texture,  over- 
firm  body  and  imperfect  flavor. 

(3)  Too  little  salt  is  shown  by  insipidity  of  taste. 


24O  MODERN    METHODS   OF  TESTING   MILK 

It  is  usually  accompanied  by  bitter  flavor  and  porous 
texture. 

Appearance. — This  term  refers  to  the  general  ap- 
pearance of  the  cheese  to  the  eye  in  respect  to  uni- 
formity, neatness  and  cleanliness.  It  may  also  include 
the  boxing.  One  system,  as  in  the  case  of  butter,  de- 
scribes under  "finish"  the  appearance  of  the  cheese,  and 
under  "packages"  the  boxing;  and  we  will  follow  this 
method  here. 

Testing  appearance. — When  the  cover  of  the  box 
is  removed  for  sampling,  in  the  case  of  boxed  cheese, 
the  appearance  of  the  cheese  is  noticed  and  the  box 
itself  is  examined.  Cleanliness  and  neatness  are 
the  points  to  observe  in  judging  appearance. 

Terms  describing  appearance. — The  general  terms 
used  in  describing  appearance  are  (i)  finish  and  (2) 
package. 

(1)  Finish  in  appearance,  in  order  to  be  perfect, 
must  meet  the  following  requirements :  The  rind  must 
be  smooth,  even  in  color,  free  from  cracks  and  fairly 
hard.     The  bandage  must  be  without  wrinkles  and 
must  be  neatly  rounded  over  the  edges  about  an  inch 
and  a  half  on  each  end  of  the  cheese.     The  sides  of 
the  cheese  should  be  straight  and  of  uniform  height 
all  around. 

The  faults  of  appearance  in  finish  are  as  follows,  the 
terms  being  self-descriptive:  (i)  Cracks,  (2)  light 
spots,  (3)  roughness  in  rind,  (4)  uneven  edges,  (5) 
wrinkles  in  bandage,  (6)  lack  of  uniformity  in  ends 
and  in  height,  (7)  bulging  out  at  sides  or  ends. 

(2)  Package. — The  packages  or  boxes  are  regarded 
as  perfect  when  of  good  material,  well  made,  strong, 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  £4! 

clean,  close-fitting,  uniform  in  size  and  in  undamaged 
condition. 

SCORING  CHEESE 

The  qualities  described  in  the  preceding  pages  are 
used  for  judging  and  fixing  tthe  commercial  value  of 
cheese. 

Scale  of  points. — The  following  scale  of  points  is 
in  use  in  many  places,  the  numbers  indicating  perfect 
quality  in  each  case  and  the  totals  aggregating  100: 

Flavor,  50  Body,  15  Salt,     5 

Texture,  15  Color,  10  Appearance,     5 

In  the  practice  of  many  markets,  salt  is  omitted  and 
appearance  is  given  10  points. 

Method  of  scoring. — The  general  procedure  is  es- 
sentially the  same  as  that  already  described  in  connec- 
tion with  butter  (p.  160). 

Method  of  grading  cheese. — The  same  general  prin- 
ciples apply  as  in  grading  butter  (p.  231  ).  One  class- 
ification is  into  (i)  "fancy,"  (2)  "firsts,"  and  (3) 
"seconds."  In  the  Canadian  market,  there  are  first, 
second  and  third  grades. 

Score-cards  for  cheese  can  be  prepared  in  a  manner 
similar  to  those  previously  suggested  for  butter  (p.  230) . 

As  in  the  case  of  butter,  the  testing,  scoring  and 
grading  of  cheese  demand  good  judgment  trained  by 
experience.  The  sense  of  smell  and  touch  must  be 
well  developed. 

No  formal  classification  or  grading  of  cheese  is 
made  by  the  New  York  Mercantile  Exchange,  as  is 
done  in  the  case  of  butter. 


CHAPTER  XVIII 

Methods  of   Commercial   Testing  and  Scoring 
of  Milk  and  Cream 

In  the  past  few  years,  there  has  been  a  growing 
sentiment  that  some  method  of  testing  the  commer- 
cial value  of  milk  and  cream,  similar  to  that  used  in 
judging  butter  and  cheese,  is  much  needed.  Some 
helpful  work  has  been  done  in  this  direction  by  the 
Dairy  Division  of  the  U.  S.  Department  of  Agricul- 
ture. The  writer  believes  an  efficient  system  will  be 
developed  in  the  near  future,  and,  as  a  basis  for  such 
a  system,  the  present  discussion  is  offered. 

For  convenience  of  treatment,  we  will  classify  milk 
and  cream  according  to  the  purposes  for  which  they 
are  used,  as  follows:  (i)  Market  milk  and  cream, 
when  sold  for  direct  consumption  as  such.  (2)  Cream- 
ery milk  and  cream,  when  used  for  butter-making. 
(3)  Cheese- factory  milk,  when  used  for  cheese-ma- 
king. (4)  Certified  and  standardized  milk,  when  pro- 
duced under  specific  sanitary  conditions  and  reaching 
a  guaranteed  standard  of  composition. 

TERMS    USED    IN    DESCRIBING    QUALITIES    OF 
MARKET    MILK 

The  qualities  that  are  selected  as  a  basis  in  the  com- 
mercial testing  and  scoring  of  milk  are  the  following : 
(i)  Composition,  (2)  keeping-power,  (3)  flavor,  and, 
we  may  add,  though  of  minor  importance,  (4)  color, 

242 


COMMERCIAL   TESTING   OF    MILK   AND   CREAM      243 

and  (5)  appearance.  For  all  practical  purposes  color 
and  package  can  be  omitted.  In  educational  competi- 
tions they  may  be  included. 

Composition. — By  composition  is  meant  the  per 
cent,  of  fat  and  of  solids-not-fat  in  milk.  The  com- 
position of  milk,  other  things  being  equal,  is  the  direct 
and  only  practicable  measure  of  value  as  food,  and 
this  must  constitute  an  important  factor  in  judging 
the  value  of  market  milk. 

Testing  composition. — The  percentages  of  fat  and 
of  solids-not-fat  are  found  in  the  manner  described 
on  p.  57  and  p.  185. 

Terms'  describing  composition. — Only  two  terms 
need  to  be  used  in  describing  the  composition  of  milk : 
(i)  perfect  and  (2)  defective. 

(1)  Perfect,  as  applied  to  testing  and  scoring  milk, 
means  milk  containing  not  less  than  4  per  cent,  of  fat 
and  not  less  than  9  per  cent,  of  solids-not-fat. 

(2)  Defective  applies  to  milk  containing  less   fat 
or  solids-not-fat  than  required  for  milk  of  "perfect" 
composition. 

The  figures  selected  to  indicate  milk  "perfect"  in 
composition  represent  as  nearly  as  possible  normal 
milk  of  average  composition.  Injustice  would  obvi- 
ously be  done  by  selecting  4.5  or  5  per  cent,  as  the 
amount  of  fat  to  represent  milk  perfect  in  compo- 
sition. It  would,  on  the  other  hand,  be  very  unsatis- 
factory to  take  a  so-called  legal  standard  as  repre- 
senting perfect  composition,  because  it  is  not  a  stand- 
ard at  all  but  simply  a  method  of  prescribing  the  low- 
est permissible  amounts  of  fat  and  solids  that  will  be 
legally  tolerated  in  milk. 


244  MODERN    METHODS   OF  TESTING   MILK 

Keeping-power  is  an  expression  used  to  indicate 
in  a  general  way  the  length  of  time  milk  remains 
sweet  and  palatable  for  direct  consumption.  In  esti- 
mating the  commercial  value  of  milk,  this  is  an  im- 
portant factor;  since  milk  that  is  sour  or  otherwise 
unpalatable,  or  milk  containing  the  products  of  any 
form  of  undesirable  fermentation,  is  comparatively 
valueless  for  direct  consumption,  however  rich  it  may 
be  in  fat  and  other  solids.  Keeping-power  is  a  matter 
of  much  importance  in  warm  weather,  especially  in 
the  case  of  milk  that  is  transported  long  distances 
before  reaching  the  consumer. 

Testing  keeping-power. — The  keeping-power  of 
milk  is  tested  by  making  determinations  of  (i)  the 
acidity  (p.  131),  (2)  the  dirt  in  suspension  (p.  163), 
(3)  the  fermentation  test  (p.  155),  and  (4)  the  num- 
ber of  bacteria  (when  practicable). 

Terms  describing  keeping-power. — The  terms  used 
in  describing  the  keeping-power  of  milk  are  (i)  per- 
fect, (2)  acidity,  (3)  dirt  it?  suspension,  (4)  unde- 
sirable fermentations,  and  (5)  number  of  bacteria  per 
cubic  centimeter. 

(1)  Perfect. — Milk   is    called   perfect   in   keeping- 
power  (a)  when  its  acidity  is  not  above  0.18  per  cent., 
(b)  when  it  contains  no  dirt  in  suspension,  (c)  when 
the  fermentation  test  reveals  nothing  abnormal,  and 
(d)    when  the  number  of  bacteria  does  not  exceed 
100,000  per  cubic  centimeter. 

(2)  Acidity  is  used  to  mean  the  amount  of  appar- 
ent total  acid  calculated  as  lactic,  as   shown  by  the 
amount  of  alkali  neutralized.     For  discussion  of  the 
relation  of  acidity  to  the  temperature  and  cleanliness 
of  milk,  see  pp.  154. 


COMMERCIAL   TESTING   OF    MILK   AND    CREAM      245 

(3)  Dirt  in  suspension.     The  amount  of  dirt  sus- 
pended in  milk  may  usually  be  regarded  as  a  rough 
measure  of  the  germ  content  or  cleanliness  of  milk, 
since  the  visible  dirt  we  find  in  milk  is  generally  the 
same  in  source  and  kind. 

(4)  Undesirable  fermentations  refer  to  the  results 
of  the  fermentation  test.    They  may  reveal  themselves 
in    causing   porous,    spongy    curd    and    in    producing 
offensive  odors. 

(5)  Number  of  bacteria  per  cubic  centimeter  is  a 
self-descriptive  term. 

Flavor,  applied  to  milk,  is  used  to  mean  the  odor 
and  taste.  The  abnormal  odors  and  tastes  noticeable 
in  market  milk,  otherwise  good,  come  from  three 
sources :  ( i )  From  certain  things  eaten  by  the  cow, 
as  leeks,  onions,  rag-weed,  cabbage,  etc.  (2)  From 
the  direct  absorption  of  strong-smelling  substances 
present  in  the  air  surrounding  the  milkr  such  as  ma- 
nure, tobacco  smoke,  ensilage,  etc.  (3)  From  stable 
filth  dropping  bodily  into  the  milk. 

Testing  flavor. — This  is  done  by  tasting  and  smell- 
ing the  milk.  The  presence  of  abnormal  odors  can  be 
more  readily  perceived  by  heating  the  milk  for  a  few 
minutes  to  100°  F.  in  a  closed  bottle  or  jar  and  then 
smelling  at  once  on  opening  the  vessel. 

Terms  describing  flavor. — The  following  terms 
may  be  used  in  describing  the  flavor  of  market  milk: 
(i)  Perfect,  (2)  stable  or  cow  manure,  (3)  cowy  or 
animal,  (4)  weedy,  caused  by  leeks,  rag-weed,  etc., 

(5)  vegetable,  such  as  cabbage,  turnip,  ensilage,  etc., 

(6)  bitter,  (7)  fishy,  (8)  sour,  (9)  tainted. 

(i)   Perfect  flavor  in  market  milk  is  indicated  by 


246  MODERN    METHODS    OF    TESTING    MILK 

freedom  from  all  traces  of  abnormal  odor  and  taste. 
There  should  be  no  marked  odor  and  no  trace  of  any 
offensive  smell.  The  taste  should  be  palatable,  slightly 
saline  and  rich,  without  any  unpalatable  after-taste. 
It  should  not  be  flat  or  insipid. 

The  other  terms  are  mostly  self-descriptive.  Their 
number  could  be  extended  to  cover  more  minute  de- 
tails. The  term  tainted  is  used  to  cover  miscellaneous 
offensive  flavors  not  included  under  other  terms. 

Color  in  relation  to  the  testing  and  scoring  of  mar- 
ket milk  explains  itself.  It  is  in  itself  of  little  prac- 
tical importance  and  may  usually  be  omitted  except  in 
case  of  educational  competitions. 

Testing  color. — The  milk  is  examined  for  color  by 
direct  inspection  in  a  clear  light. 

Terms  describing  color. — In  describing  the  color 
of  market  milk,  the  following  terms  may  be  used: 
(i)  Perfect,  (2)  white,  (3)  bluish,  (4)  high  color, 
(5)  reddish. 

(i)  Perfect  as  applied  to  color  in  milk  indicates  a 
yellowish  color,  not  too  pronounced,  strikingly  differ- 
ent from  the  white  or  bluish  color  of  skim-milk,  but 
not  as  deep  as  the  color  of  cream. 

The  other  terms  explain  themselves.  High  color 
may  be  caused  by  artificial  coloring,  usually  producing 
a  reddish  tint. 

Appearance. — This  term  refers  to  the  appearance 
of  the  can,  bottle  or  other  vessel  containing  the  milk 
and  applies  to  these  in  respect  to  uniformity,  neatness 
and  cleanliness.  This  is  of  relatively  small  practical 
importance  and  may  usually  be  omitted  in  commercial 
work.  It  finds  a  use  in  educational  competitions. 


COMMERCIAL   TESTING   OF    MILK   AND    CREAM      247 
SCORING  MARKET  MILK 

The  qualities  described  above  are  intended  for  use 
in  the  commercial  judging  and  scoring  of  market 
milk.  For  practical  purposes  it  will  be  sufficient  ordi- 
narily to  make  use  of  the  first  three  qualities  men- 
tioned, viz:  (i)  composition,  (2)  keeping-power,  and 
(3)  flavor. 

Scale  of  points. — In  fixing  a  scale  of  points,  we  have 
a  score  of  100  to  distribute  among  the  three  qualities 
last  mentioned.  How  many  points  of  the  100  shall  be 
assigned  to  each?  Here  is  a  chance  for  wide  varia- 
tion of  opinion.  In  actual  experience,  flavor  does  not 
hold  the  same  important  relation  to  market  milk  that 
it  does  to  cheese  and  butter.  A  flavor  that  is  imper- 
ceptible in  the  ordinary  consumption  of  milk  usually 
becomes  concentrated  in  the  process  of  butter-making 
or  cheese-making  and  seriously  affects  the  quality  of 
the  final  product.  A  flavor  must  be  very  bad  to  render 
milk  useless  for  cooking  or  for  purposes  other  than 
direct  drinking.  Hence,  flavor  should  not  receive  so 
high  a  score  in  the  case  of  market  milk  as  in  the  case 
of  butter  or  cheese.  On  the  other  hand,  composition 
should  receive  a  relatively  high  score,  since,  other 
things  being  equal,  it  alone  governs  the  relative  values 
of  different  milks.  The  importance  of  keeping-power 
has  already  been  considered.  For  the  various  reasons 
given,  the  following  scale  of  points  is  suggested  as  a 
desirable  one  for  practical  use : 

Composition 40 

Keeping-power 30 

Flavor 30 


248  MODERN    METHODS   OF   TESTING    MILK 

The  numbers  indicate  perfect  quality  in  each  case 
and  the  totals  aggregate  100.  The  numbers  assigned 
could  be  varied  considerably  and  still  give  equally 
satisfactory  results  in  practise. 

Method  of  scoring. — The  milk  is  examined  in  the 
manner  previously  described  and  defects  are  indicated 
by  making  deductions  from  the  perfect  score  in  the 
following  manner: 

(1)  Composition. — The  perfect  score  of  40  points 
is  reduced  one  point  for  each  o.i  per  cent,  below  4  per 
cent,  of  fat  and  one  point  for  each  o.i  per  cent,  below 
9  per  cent,  of  solids-not-fat. 

(2)  Keeping-power. — The   perfect   score   of   30   is 
to  be  reduced  (a)  one  point  for  each  o.oi  per  cent,  of 
acidity  above  0.18;   (b)   a  certain  number  of  points, 
according  to  the  judgment  of  the  examiner,  for  dirt 
in  suspension;  (c)  a  certain  number  of  points  for  any 
abnormal  results  shown  by  the  fermentation  test;  and 
(d)  one  point  for  each  100,000  bacteria  above  ioo;ooo 
in  i  cubic  centimeter  of  milk,  when  this  determination 
is  made. 

(3)  Flavor. — The  perfect  score  of  30  is  reduced  by 
the  presence  of  abnormal  odors  or  tastes,  the  examiner 
using  his  judgment  as  to  the  amount  of  reduction. 

JUDGING  MILK  FOR  MANUFACTURE   OF 
BUTTER  AND   CHEESE 

For  milk  that  is  to  be  used  for  butter-making  or 
cheese-making,  a  somewhat  different  method  is  sug- 
gested for  judging  and  scoring.  Since  such  milk  is 
or  should  be  paid  for  on  the  basis  of  the  fat,  the  sys- 


COMMERCIAL   TESTING   OF    MILK   AND    CREAM      249 

tern  of  judging  and  scoring  should  be  such  as  to  .affect 
the  value  or  the  amount  of  the  fat  for  which  payment 
is  received.  Such  a  method  is  given  in  the  following 
statements : 

(1)  Score  the  milk  directly  for  two  qualities  only, 
(a)    keeping-power  and   (b)   flavor.     For  perfection, 
allow  50  points  for  keeping^power  and  50  points  for 
flavor. 

(2)  From  the  total  amount  (pounds)   of  fat  con- 
tained in  the  milk  furnished  by  each  patron,  deduct, 
according  to  the  results  of  scoring,  a  certain  amount 
of  fat,  which  is  found  by  multiplying  the  total  amount 
of  fat  in  the  milk  by  0.25  per  cent,  and  this  result  by 
the  number  of  points  scored  below  100. 

(3)  Use  the  number  of  pounds  of  fat  thus  found 
as  the  actual  amount  of  fat  on  which  to  base  dividends. 
To  illustrate,  a  patron  furnishes  1,000  pounds  of  milk, 
containing  4  per  cent,  of  fat,  which  scores  90  in  keep- 
ing-power and  flavor.    What  deduction  shall  be  made 
from  the  fat  for  the  score  of  90?    The  amount  (1,000 
pounds)  of  milk  furnished  contains  40  pounds  of  fat. 
This  number  (40)  multiplied  by  0.25  per  cent.  (Rule 
J>  P-  253)  equals  o.i  pound  of  fat,  which  multiplied  by 
10,  the  number  of  points  scored  below  100,  equals  I 
pound.    The  total  amount  (40  pounds)  of  fat,  dimin- 
ished by  the  subtraction  of  I,  leaves  39  pounds,  which 
amount  would  be  used  as  a  basis  in  making  this  pa- 
tron's dividend. 

The  judging  of  flavor  and  keeping-power  is  carried 
out  as  previously  described  for  market  milk.  In 
cheese-making,  it  is  important  to  make  full  use  of  the 
fermentation  test  (p.  155). 


25O  MODERN    METHODS   OF   TESTING    MILK 

COMMERCIAL  TESTING  AND  SCORING  OF  CER- 
TIFIED AND  STANDARDIZED  MILK 

Certified  milk  usually  guarantees  (i)  the  per  cent 
of  fat,  (2)  the  per  cent,  of  total  solids  or  solids-not- 
fat,  and  (3)  bacteria  below  a  specified  number.  Stand- 
ardised milk  usually  guarantees  only  the  per  cent,  of 
fat. 

The  examination  and  scoring  of  certified  or  of  stand- 
ardized milk  are  conducted  in  the  same  manner  as  in 
the  case  of  market  milk,  except  that  the  scoring  is 
based  upon  the  guarantees,  so  far  as  these  are  given. 
The  guaranteed  per  cent,  of  fat  and  of  solids-not-fat 
and  the  number  of  bacteria  are  to  be  taken  as  repre- 
senting the  perfect  score  in  place  of  the  figures  given 
above  for  market  milk,  and  deductions  from  the  per- 
fect score  for  defects  are  made  on  the  basis  of  the 
guarantees.  For  example,  if  a  certified  milk  is  guar- 
anteed to  contain  5  per  cent,  of  fat,  then,  in  order  to 
score  40  in  composition,  the  milk  must  contain  5  per 
cent,  of  fat  and,  in  case  of  any  shortage,  a  proportion- 
ate deduction  should  be  made  from  the  perfect  score 
of  40. 

COMMERCIAL    TESTING    AND    SCORING    OF 
CREAM 

Market  cream  is  that  which  is  sold  for  direct  con- 
sumption. The  method  of  examining  and  scoring 
market  cream  is  essentially  the  same  as  in  the  case 
of  market  milk.  In  composition,  cream  is  not  exam- 
ined or  scored  for  solids  but  for  fat  only.  Another 
quality  might  be  added  in  case  of  cream,  that  of  body, 


COMMERCIAL   TESTING   OF    MILK   AND    CREAM      2$I 

by  which  is  meant  the  consistency  of  the  cream,  espe- 
cially with  reference  to  the  presence  or  absence  of 
lumps,  complete  evenness  of  consistency  being  required 
for  perfection  of  body. 

In  composition,  not  less  than  20  per  cent,  of  fat 
should  be  used  as  a  basis  for  perfection  and  from  the 
perfect  score  of  40  is  deducted  one  point  for  each  0.5 
per  cent,  of  fat  below  20.  Acidity  and  flavor  are  of 
special  importance  in  market  cream.  The  acidity 
should  not  be  allowed  to  be  above  0.2  per  cent,  for 
perfect  cream. 

Creamery  cream  is  that  which  is  intended  for  but- 
ter-making. The  same  general  procedure  is  employed 
as  in  the  case  of  milk  that  is  to  be  used  for  butter- 
making,  which,  adapted  to  cream,  is  as  follows : 

1 i )  Score  the  cream  directly  for  two  qualities  only, 
(a)    keeping-power  and    (b)    flavor.     For  perfection 
allow  50  points  for  each  quality. 

(2)  From  the  total  amount   (pounds)   of  fat  con- 
tained in  the  cream  furnished  by  each  patron  deduct, 
according  to  the  results  of  scoring,  a  certain  amount 
of  fat,  which  is  found  by  multiplying  the  total  amount 
of  fat  in  the  cream  by  0.25  per  cent,  and  this  result 
by  the  number  of  points  scored  below  100. 

(3)  Use  the  number  of  pounds  of  fat  thus  found  as 
a  basis  for  making  dividends. 

To  illustrate,  a  patron  furnishes  500  pounds  of 
cream,  containing  20  per  cent,  of  fat,  which  scores  90 
in  keeping-power  and  flavor.  What  deduction  shall 
be  made  from  the  fat  for  the  score  of  90?  The  amount 
(500  pounds)  of  cream  furnished  contains  100  pounds 
oi  fat.  This  number  (100)  multiplied  by  0.25  per 


252  MODERN    METHODS    OF    TESTING    MILK 

cent.  (Rule  i,  p.  253)  equals  0.25  pound  of  fat,  which 
multiplied  by  10,  the  number  of  points  scored  below 
100,  equals  2.5  pounds.  The  total  amount  (100  pounds) 
of  fat,  diminished  by  the  subtraction  of  2.5,  leaves 
97.5  pounds  of  fat,  which  amount  would  be  used  as  a 
basis  in  making  this  patron's  dividend. 


CHAPTER   XIX 

Arithmetic  of  Milk  and  Milk  Products 

In  connection  with  the  testing  of  milk  and  milk 
products,  especially  in  some  of  the  practical  applica- 
tions, various  arithmetical  calculations  are  often  nec- 
essary. Special  attention  may  need  to"  be  given  to  the 
methods  employed  in  solving  such  problems  as  are 
presented,  and  a  few  pages  are  here  devoted  to  the 
treatment  of  some  of  the  more  common  problems  in 
a  systematic,  comprehensive  form,  convenient  for  ready 
reference.  In  creameries,  cheese- factories,  etc.,  where 
much  arithmetical  work  is  involved  in  making  divi- 
dends, saving  of  time  is  effected  by  using  calculations 
or  tables,  which  are  published  in  book  form. 

I.  FINDING  WEIGHT  OF  ANY  CONSTITUENT 

Rule. — To  find  the  weight  of  any  constituent  in  milk 
or  milk  products,  when  the  weight  of  the  milk  or  its 
product  and  the  per  cent,  of  the  constituent  are  known, 
multiply  the  weight  by  the  number  indicating  the  per 
cent,  of  the  constituent  and  divide  the  result  by  100. 
Example:  How  many  pounds  of  fat  in  675  pounds 
-of  milk  testing  4.6  per  cent,  of  fat?  675X4-6  =  31.05, 
the  number  of  pounds  of  fat. 


253 


254  MODERN    METHODS   OF  TESTING   MILK 

EXAMPLES  FOR  PRACTICE 

(1)  How  many  pounds  of  fat  in  2,000  pounds  of 
cheese  containing  35  per  cent,  of  fat? 

(2)  How  much  water  in   1,000  pounds  of  butter 
containing  14.5  per  cent,  of  water? 

(3)  How  many  grams  of  milk-sugar  are  there  in 
500  grams  of  milk  containing  5   per  cent,   of  milk- 
sugar? 

(4)  How   much   fat   is   there   in    1,200  pounds   of 
cream  testing  44  per  cent,  of  fat? 

(5)  How  much  fat  is  there  in  5,000  pounds  of  skim- 
milk  testing  .15  per  cent,  of  fat? 


2.  FINDING  PER   CENT.    OF  ANY   CONSTITUENT 

Rule. — To  find  the  per  cent,  of  any  constituent  in 
milk,  etc.,  when  the  weight  of  the  milk,  etc.,  and  the 
weight  of  the  constituent  are  known,  multiply  the 
weight  of  the  constituent  by  100  and  divide  the  result 
by  the  weight  of  the  milk,  etc.  Example:  What  is 
the  per  cent,  of  fat  in  675  pounds  of  milk  containing 
31.05  pounds  of  fat?  31'°^IO°  =  4.6  per  cent. 


EXAMPLES  FOR  PRACTICE 

(1)  What  is  the  per  cent,  of  fat  in  120  pounds  of 
butter  containing  96  pounds  of  fat? 

(2)  What  is  the  per  cent,  of  water  in  600  pounds 
of  cheese  containing  210  pounds  of  water? 


ARITHMETIC   OF   MILK  AND   MILK   PRODUCTS     255 

3.  FINDING  PER  CENT.  OF  SOLIDS  IN  MILK 

Rule. — To  find  the  per  cent,  of  solids  in  milk  when 
the  Quevenne  lactometer  reading  and  the  per  cent, 
of  fat  are  known,  divide  the  lactometer  reading  by  4, 
and  to  the  result  add  the  per  cent,  of  fat  multiplied  by 
1.2.  (See  p.  137.) 

4.    FINDING    PER    CENT.    OF    SOLIDS-NOT-FAT 
IN  MILK 

Rule. — To  find  the  per  cent,  of  solids-not-fat  in 
milk  when  the  Quevenne  lactometer  reading  and  the 
per  cent,  of  fat  are  known,  divide  the  lactometer  read- 
ing by  4,  and  to  the  result  add  the  per  cent,  of  fat 
multiplied  by  .2.  (See  p.  137.) 

EXAMPLES  FOR  PRACTICE  UNDER  RULES 
3  AND  4 

(1)  What  is  the  per  cent,  of  solids  in  milk  testing 
4  per  cent,  of  fat  and  showing  a  lactometer  reading 
of  32? 

(2)  What  is  the  per  cent,  of  solids-not-fat  in  the 
same  milk  as  in   ( i )  ? 

(3)  What  is  the  per  cent,  (a)  of  solids  and  (b)  of 
solids-not-fat  in  a  milk  testing  2.5   per  cent,   of  fat 
and  showing  a  lactometer  reading  of  27? 

(4)  What  is  the  per  cent,  (a)  of  solids  and  (b)  of 
solids-not-fat  in  milk  testing  .2  per  cent,  of  fat  and 
showing  a  lactometer  reading  of  36? 


256  MODERN    METHODS   OF  TESTING   MILK 

5.  FINDING  THE  "OVERRUN"  IN  BUTTER- 
MAKING 

The  weight  of  butter  produced  is  greater  than  the 
amount  of  fat  in  the  milk  or  cream  from  which  the 
butter  is  obtained,  because  butter,  in  addition  to  its 
fat,  contains  water,  salt  and  curd.  Such  excess  is 
called  the  "overrun"  and  may  be  readily  ascertained 
by  finding  the  yield  of  butter  for  one  pound  of  fat. 
While  some  milk-fat  is  lost  in  the  skim-milk  and  but- 
termilk and  in  handling  during  butter-making,  enough 
water,  salt  and  curd  are  added  to  the  fat  to  make  up 
these  losses  and  something  more.  The  amount  of  but- 
ter yield  for  a  pound  of  fat  in  milk  or  cream  neces- 
sarily varies  with  the  variation  of  losses  of  fat  in  skim- 
milk  and  in  butter-making  and  the  amount  of  water, 
salt,  etc.,  retained  in  the  butter.  Hence  the  "overrun" 
varies.  When  the  operations  of  skimming  milk  and 
butter-making  are  properly  managed,  one  pound  of 
fat  in  milk  produces  about  1.17  (about  I  1-6)  pounds 
of  butter.  Hence,  the  "overrun"  is  .17  or  one-sixth, 
(17  per  cent).  The  "overrun"  in  case  of  cream  aver- 
ages about  .03  higher  than  in  case  of  milk,  according 
to  Hills. 

Rule. — To  find  the  "overrun"  when  the  weight 
of  butter  made  from  a  given  amount  of  milk  or  cream 
and  the  per  cent,  of  fat  in  the  milk  or  cream  are  known, 
find  the  number  of  pounds  of  fat  in  the  milk  or  cream 
by  Rule  i,  and  divide  the  weight  of  butter  by  the  weight 
of  fat.  From  the  result  subtract  i.  Example:  What 
is  the  "overrun"  in  case  of  milk  testing  4  per  cent,  of 


ARITHMETIC   OF   MILK   AND   MILK   PRODUCTS      257 

fat,  when  we  make  135  pounds  of  butter  from  3,000 
pounds  of  milk?  Applying  Rule  i,  -3°°^4  =120,  pounds 
of  fat  in  milk;  and  135-^120=1.125  (i^)  pounds. 
1.125 — i=.i25  (12.5  per  cent.)  or  y%.  Therefore,  the 
"overrun"  is  .125  or  l/%  pound,  that  is,  for  each  pound 

of  fat  in  milk  there  will  be  made  il/%  pounds  of  butter. 

i 

6.  FINDING  THE  YIELD  OF  BUTTER 

Rule. — To  find  the  yield  of  butter  when  the  per 
cent,  of  fat  in  milk  and  the  weight  of  milk  are  known, 
find  the  number  of  pounds  of  fat  in  milk  by  Rule  i 
and  multiply  this  result  by  1.17  or  i  1-6.  Example: 
How  much  butter  is  made  from  1,000  pounds  of  milk 
containing  4  per  cent,  of  fat?  Applying  Rule  i, 
1000x4  _  ^  p0unc[s  Of  faf-  jn  miik;  and  40x1.17= 

46.8,  pounds  of  butter  yield. 

In  the  case  of  cream  apply  the  foregoing  rule,  ex- 
cept to  multiply  by  1.20  instead  of  1.17. 

The  application  of  this  rule  finds  use  in  checking 
creamery  work.  If  the  yield,  in  case  of  milk,  is  not 
in  proportion  to  an  "overrun'*  of  15  to  17  per  cent, 
and  in  case  of  cream,  20  per  cent.,  one  should  ascer- 
tain why  and  then  correct  such  faults  as.  are  found  to 
exist  in  the  form  of  losses  of  fat  or  retaining  too  little 
water.  When  the  proportion  of  butter  to  fat  greatly 
exceeds  1.17  in  the  case  of  milk,  too  much  water  is 
retained  in  the  butter,  or  else  the  fat-test  is  improperly 
made  or  the  results  purposely  read  too  low. 


258  MODERN    METHODS   OF   TESTING    MILK 

EXAMPLES  FOR  PRACTICE  UNDER  RULES 
5  AND  6 

(1)  How  much  butter  should  be  made  from  5,000 
pounds  of  milk  testing  5  per  cent,  of  fat? 

(2)  What  is  the  "overrun"  when  4,000  pounds  of 
milk,  testing  4  per  cent,  of  fat,  yield  180  pounds  of 
butter? 

(3)  A  butter-maker  has  10,000  pounds  of  milk,  test- 
ing 4  per  cent,  of  fat;  in  skimming  this,  he  produces 
8,000  pounds  of  skim-milk,  testing  .15   per  cent,   of 
fat.     After  churning,  he  has  1,600  pounds  of  butter- 
milk testing  .2  per  cent,  of  fat.     The  loss  of  fat  in 
handling  the  cream  and  making  the  butter  amounts  to 
4  pounds,    (a)    How  much  fat  is  left  in  the  butter? 

(b)  How  many  pounds  of  butter  should  be  made? 

(c)  What  is  the  "overrun"  if  he  produces  450  pounds 
•of  butter? 

(4)  How  much  butter  should  be  made  from  1,000 
pounds  of  cream  testing  35  per  cent,  of  fat? 

7.  FINDING  YIELD   OF   CHEESE   FOR  MILK-FAT 

Rule. — To  find  the  yield  of  green  cheese  for  a  pound 
of  fat  in  milk  when  the  weight  of  the  cheese  made 
from  a  given  amount  of  milk  and  the  per  cent,  of  fat 
in  milk  are  known,  find  the  number  of  pounds  of  fat 
in  milk  by  Rule  i,  and  divide  the  weight  of  cheese  by 
the  weight  of  fat.  Example:  How  much  cheese  is 
made  for  one  pound  of  fat  in  milk,  testing  4  per  cent, 
of  fat,  when  we  make  63  pounds  of  cheese  from  600 
pounds  of  milk?  Applying  Rule  i,  6o0^4  =  24 
pounds  of  fat  in  milk;  63-5-24=2.67  pounds  of  cheese 


ARITHMETIC  OF  MILK  AND  MILK  PRODUCTS        259 

made  for  one  pound  of  fat  in  milk.  In  connection  with 
cheese,  this  is  the  same  kind  of  relation  as  the  "over- 
run" in  butter.  In  cheese-making  a  pound  of  fat 
in  milk  has  added  to  it  enough  casein,  water,  salt, 
etc.,  to  increase  the  weight  from  i  of  fat  to  2.7  (more 
or  less)  pounds  of  cheese. 

i 

8.  FINDING  YIELD  OF  CHEESE  FROM  FAT  IN 
MILK 

Rule. — To  find  the  yield  of  green  cheese  from  100 
pounds  of  milk  when  the  per  cent,  of  fat  in  milk  is 
known,  multiply  the  per  cent,  of  fat  in  milk  by  2.7.  Ex- 
ample: How  much  cheese  should  be  made  from  100 
pounds  of  milk  testing  3.7  per  cent,  of  fat?  3.7x2.7= 
9.99  pounds. 

This  rule  applies  only  to  normal  milk  containing 
3.6  to  3.8  per  cent,  of  fat.  For  milk  containing  fat 
above  3.8  per  cent.,  the  results  are  usually  too  high; 
and  for  milks  containing  less  than  3.6  per  cent,  of 
fat,  the  results  are  usually  too  low. 

9.  FINDING  YIELD  OF  CHEESE  FROM  FAT  AND 
CASEIN  IN  MILK 

Rule. — To  find  the  yield  of  green  cheese,  containing 
37  per  cent,  of  water,  from  100  pounds  of  milk  when 
the  per  cent,  of  fat  and  of  casein  in  milk  is  known,  add 
the  per  cent,  of  casein  and  of  fat  and  multiply  the  sum 
by  1.63.  Example:  How  much  cheese  can  be  made 
from  100  pounds  of  milk  containing  4  per  cent,  of 
fat  and  2.5  per  cent,  of  casein?  (4+2.5 )xi. 63=10.60 
pounds  of  green  cheese. 


2<5O  MODERN   METHODS  OF  TESTING   MILK 

10.  FINDING  PER  CENT.  OF  CASEIN  IN  MILK 
FROM  FAT 

Rule. — To  find  the  per  cent,  of  casein  in  milk  when 
the  per  cent,  of  fat  is  known,  subtract  3  from  the  per 
cent  of  fat  in  milk,  multiply  the  result  by  .4  and  add 
this  result  to  2.1.  Example:  How  much  casein  is  there 
in  milk  containing  4.5  per  cent,  of  fat?  (4.5 — 3)  x.4+ 
2.1=2.70  per  cent,  of  casein. 

This  rule  is  based  upon  the  writer's  work,  showing 
that  milk  testing  3  per  cent,  of  fat  contains  an  average 
of  about  2.1  per  cent,  of  casein,  and  that  the  casein  in- 
creases, on  an  average  0.4  per  cent,  when  the  per  cent, 
of  milk  increases  i  per  cent,  above  3.  This  is  especially 
true  of  milks  ranging  from  3  to  4.5  per  cent,  of  fat 
when  the  milk  is  produced  at  the  same  stage  of  lacta- 
tion. In  the  later  stages  of  lactation  the  ratio  of  ca- 
sein to  fat  is  usually  greater  than  is  indicated  by  this 
rule.  (See  p.  12). 

The  above  rule  is  based  upon  work  done  in  making 
a  careful  study  in  New  York  State  of  the  milk  of  each 
of  50  different  herds  of  cheese-factory  cows  during  one 
season  (May  to  October).  Taking  the  average  of  the 
entire  season  it  was  found  that  80  per  cent,  of  the 
results  obtained  by  the  method  of  calculation  differed 
from  those  given  by  the  chemical  method  by  less  than 
o.i  per  cent. 

The  above  rule  can  be  used  in  finding  the  amount 
of  casein  and  albumin  together,  the  factor  2.9  being 
added  instead  of  2.1. 

The  rule  will  be  found  useful  by  physicians  in  modi- 
fying milk  for  infant  feeding. 


ARITHMETIC  OF  MILK  AND  MILK  PRODUCTS       26l 

11.  FINDING  YIELD  OF  CHEESE  FROM  FAT  AND 
CALCULATED  CASEIN 

When  the  per  cent,  of  fat  only  is  known,  the  amount 
of  casein  can  be  estimated  in  the  manner  given  in  Rule 
10  and  this  figure  used  for  casein  in  Rule  9 ;  or,  better, 
the  two  operations  of  calculating  casein  and  cheese 
yield  can  be  combined  in  one  Dimple  rule,  as  follows : 
Multiply  the  percentage  of  fat  by  2.3  and  add  1.4.  Ex- 
ample: How  much  green  cheese,  containing  37  per 
cent,  of  water,  can  be  made  from  milk  containing  4 
per  cent,  of  fat?  (4x2. 3) +1.4=10.60  pounds. 

The  subject  of  calculating  yield  of  cheese  is  fully 
discussed  in  Van  Slyke  and  Publow's  "Science  and 
Practice  of  Cheese-Making"  (pp.  211-230).  As  there 
explained,  some  of  the  formulas  that  have  been  used 
extensively  have  only  a  limited  application  when  ac- 
curacy is  considered. 

EXAMPLES  FOR  PRACTICE  UNDER  RULES 
8  TO  11 

(1)  What  is  the  per  cent,  of  casein  in  milk  contain- 
ing (a)  3-5°>  (b)  3-6o,  (c)  4,  (d)  4.4  per  cent,  of  fat? 

(2)  How  much  green  cheese  should  be  made  from 
100  pounds  of  the  different  milks  mentioned  in  the 
preceding  example?     (Apply  Rules  9,  10  and  n). 

(3)  How  much  green  cheese  should  be  made  from 
18,000  pounds  of  milk  testing  3.75  per  cent,  of  fat? 

12.   FINDING   DIVIDENDS   ON   FAT   BASIS   AT 
CREAMERIES 

Rule. — To  calculate  the  amount  of  each  patron's 
dividend  at  creameries  on  the  basis  of  the  fat  in  the 
milk,  multiply  the  amount  of  the  milk-fat  delivered  by 
each  patron  by  the  price  of  one  pound  of  fat. 


262  MODERN    METHODS   OF  TESTING   MILK 

This  rule  can  be  made  more  clear  by  considering 
the  process  in  three  separate  steps,  assuming  that  the 
creamery  is  operated  on  the  co-operative  plan. 

Step  i.  By  Rule  I  find  the  amount  of  milk- fat  fur- 
nished by  each  patron  during  the  dividend  period. 

Step  2.  Find  the  net  value  of  one  pound  of  milk- 
fat  by  dividing  the  total  net  receipts  by  the  total  num- 
ber of  pounds  of  fat  delivered  by  all  the  patrons  during 
the  dividend  period. 

Step  3.  Multiply  the  number  of  pounds  of  fat  de- 
livered by  each  patron  by  the  net 'price  received  for 
one  pound  of  fat. 

Example:  Step  i.  The  data  and  results  are  indicated 
in  tabular  form  as  follows: 


Pounds  of  Milk         Per  cent.  Pounds  of 

NAME  OP                     delivered  during           of  fat  fat  in  milk 

PATRON                     dividend  period           in  milk  delivered 

A      ....    350         x        4.0             =  14.00 

B       ....    650         x       3.6             =  23.40 

C      ....    835         x       5.2            =  43.42 

D      .     .    *     .    965          x       4.4  42.46 

E       ....  1,200          x       4.2             =  50.40 

Total  number  of  pounds  of  fat  delivered  by      

all  patrons 173-68 


Step  2.  From  the  amount  of  fat  indicated  above, 
the  amount  of  butter  made  was  195  pounds,  which 
realized  18  cents  a  pound  after  deducting  all  expenses, 
making  a  total  of  $35.10.  This  sum  divided  by  173.68, 
the  total  pounds  of  fat  delivered,  gives  20.2  cents  as 
the  net  price  received  for  each  pound  of  fat. 


ARITHMETIC   OF   MILK   AND   MILK   PRODUCTS     263 

Step  3.  The  data  and  results  are  indicated  in  tabu- 
lar form,  as  follows : 

Pounds  Net  price  A  mount  of 

NAME  OF  of  fat  received  for  fat  dividend  due 

PATRON  delivered  per  pound  each  patron 

A  .  .  14.00  x  20.2   cents       =  $2.83 

B  .  .  2340  X  =  473 

C  .  .  4342  X  =  8.77 

D  .  .  42.46  x  =  8.58 

E  .  .  50.40  x  =  10.18 

When  both  milk  and  cream  are  used  in  a  creamery, 
the  pounds  of  fat  delivered  in  the  form  of  cream  are 
found  by  applying  Step  i  above  and  then  multiplying 
the  result  by  1.02.  From  this  point  on,  the  process  of 
calculating  dividends  is  the  same  as  above  described. 

13.  FINDING  DIVIDENDS  ON  FAT  BASIS  AT 
CHEESE-FACTORIES 

Rule. — To  calculate  the  amount  of  each  patron's 
dividend  at  cheese-factories  on  the  basis  of  the  fat  in 
the  milk,  proceed  as  under  Rule  12. 

14.  FINDING  AMOUNTS  OF  MILK,  ETC.,  TO  USE 
IN  MODIFYING  NORMAL  MILK 

The  practice  of  modifying  or  standardizing  milk 
for  special  market  purposes  is  constantly  increasing. 
This  consists  in  increasing  or  decreasing  the  per  cent, 
of  fat  in  a  normal  milk.  The  per  cent,  of  fat  in  a 
normal  milk  may  be  increased  (i)  by  adding  cream, 
(2)  by  adding  milk  richer  in  fat,  or  (3)  by  skimming 
part  of  the  normal  milk  with  a  separator  and  then  put- 
ting the  cream  thus  obtained  back  into  the  rest  of  the 
normal  milk.  The  per  cent,  of  fat  in  a  normal  milk 


264  MODERN   METHODS  OF  TESTING  MILK 

may  be  decreased  without  adding  water,  (i)  by  add- 
ing skim-milk,  (2)  by  adding  milk  poorer  in  fat,  or 
(3)  by  skimming  part  of  the  milk  and  then  putting 
the  skim-milk  thus  obtained  back  into  the  rest  of  the 
normal  milk. 

Prof.  R.  A.  Pearson,  of  Cornell  University,  has  de- 
vised an  ingenious  method  by  which  one  can  accu- 
rately, quickly  and  easily  find  the  amounts  of  milk, 
cream  and  skim-milk  to  be  used  in  modifying  or  stand- 
ardizing milk  in  order  to  produce  a  milk  containing  a 
desired  per  cent,  of  milk-fat.  The  following  diagram 
and  explanation  may  serve  to  make  clearer  the  work- 
ing of  the  method  : 


Per  cent,  fat  in  milk—  A  -         -  c—  B  or  B—  C  (pounds  of  A  to  use 


Per  cent,  fat  inj 

cream,  etc.         J  -»C' .A— B  or  B— A  (pounds  of  C  to  use) 

Cream  or  skim- 
milk,  etc. 

Let  A  represent  the  per  cent,  of  fat  in  the  milk 
to  be  modified. 

Let  B  represent  the  per  cent,  of  fat  desired  in  the 
modified  milk. 

Let  C  represent  the  per  cent,  of  fat  in  the  milk, 
cream  or  skim-milk  which  is  to  be  used  in  increasing 
or  decreasing  the  per  cent,  of  fat. 

The  problem  is  to  find  in  what  proportions  we  shall 
use  the  milk,  etc.,  containing  A  and  C,  in  order  to  ob- 
tain a  product  containing  B. 

When  the  per  cent,  of  fat  in  the  normal  milk  is 
to  be  increased,  A  is  less  than  B,  while  C  is  greater 
than  B.  In  this  case,  B  minus  A  gives  the  pounds  of 


ARITHMETIC   OF    MILK   AND   MILK   PRODUCTS      265 

the  product  containing  C  to  be  used,  while  C  minus  B 
gives  the  pounds  of  milk  (A)  to  be  used  or,  expressed 
in  another  way,  the  procedure  becomes,  B — A=pounds 
of  product  containing  C  to  be  used,  and  C — B=pounds 
of  milk  (A)  to  use. 

When  the  per  cent,  of  fat  in  the  normal  milk  is 
to  be  decreased  in  the  modified  milk,  the  procedure  is 
thus  indicated:  A — B_=zpounds  of  product  containing 
C  to  be  used  and  B — C=pounds  of  milk  (A)  to  be 
used. 

The  simplicity  of  the  method  becomes  readily  ap- 
parent when  practically  illustrated. 

(i)  When  the  per  cent,  of  fat  in  milk  is  to  be  in- 
creased by  addition  of  cream  or  richer  milk.  Rule. — 
From  the  per  cent,  of  fat  desired  in  the  modified  milk 
subtract  the  per  cent,  of  fat  in  the  milk  to  be  modified, 
and  the  result  is  the  number  of  pounds  of  cream  or 
richer  milk  to  be  used.  From  the  per  cent,  of  fat  in 
the  cream  or  richer  milk  subtract  the  per  cent,  of  fat 
desired  in  the  modified  milk,  and  the  result  is  the  num- 
ber of  pounds  to  use  of  the  milk  to  be  modified.  Ex- 
ample: What  relative  amounts  of  normal  milk  and 
cream  must  be  used  to  produce  milk  containing  4.5 
(B)  per  cent,  of  fat,  when  the  normal  milk  contains 
3.5  (A)  per  cent,  of  fat  and  the  cream  25  (C)  per 
cent.  ? 

A=3.s —  C— B=2o.s  (pounds  of  milk  to  use). 

B— 4-5 

0=25 BYA=I  (pounds  of  cream  to  use). 

Cream 

The  results  mean  that  20.5  pounds  of  milk  contain- 
ing 3.5  per  cent,  of  fat,  mixed  with  i  pound  of  cream 
containing  25  per  cent,  of  fat,  will  produce  a  modified 


266  MODERN    METHODS   OF  TESTING  MILK 

milk  containing  4.5  per  cent,  of  fat.  If,  in  place  of 
cream,  a  milk  containing  more  than  3.5  per  cent,  of 
fat  were  used,  the  process  would  be  the  same. 

(a)  If  it  is  desired  to  know  how  much  such  cream 
must  be  used  in  standardizing  1,000  pounds  of  such 
milk,  divide   1,000  by  20.5    (C— B)   and  multiply  by 
i  (B — A,)  which  will  give  48.8  pounds  of  cream  to  be 
added  and  1048.8  pounds  of  the  modified  milk. 

(b)  If  it  is  desired  to  know  how  much  such  cream 
and  milk  to  use  to  make  1,000  pounds  of  the  modified 
milk,  divide   1,000  by  21.5   (C — B)  +  (B — A),  which 
is  46.5,  and  multiply  this  amount  by  20.5  (C — B)  and 
by  i    (B — A),  which  will  give  953.5  pounds  of  3.5 
per  cent,  milk  and  46.5  pounds  of  25  per  cent,  cream. 

(2)  When  the  per  cent,  of  fai  in  milk  is  to  be  in- 
creased by  removing  a  portion  of  the  milk-serum 
(skim-milk).  Rule. — From  the  per  cent,  of  fat  de- 
sired in  the  modified  milk  subtract  the  per  cent,  of  fat 
in  the  milk  to  be  modified,  and  the  result  is  the  number 
of  pounds  of  skim-milk  to  be  removed.  The  per  cent, 
of  fat  in  the  modified  milk  is  the  number  of  pounds  to 
use  of  the  milk  to  be  modified.  This  is  done  by  sep- 
arating the  cream  from  a  portion  of  the  milk  and  then 
adding  it  to  the  normal  milk.  The  skim-milk  can  be 
assumed  to  contain  practically  no  fat.  Example :  How 
much  skim-milk  should  be  removed  from  milk  con- 
taining 3.9  per  cent,  of  fat,  in  order  to  produce  a  mod- 
ified milk  containing  5  per  cent,  of  fat? 


C— O.Q 


Skim-milk 


B— C=5  (pounds  of  milk  to  use). 

B— A— i.x  (pounds  of  skim-milk  to  remove). 


ARITHMETIC   OF   MILK  AND   MILK   PRODUCTS     267 

In  this  case  we  add  nothing,  so  that  C  equals  o  and 
B  —  C=5  —  0=5.  The  results  mean  that  for  5  pounds 
of  the  milk,  we  should  remove  i.i  pounds  of  skim- 
milk,  thus  reducing  5  pounds  of  milk  containing  3.9 
per  cent,  of  fat  to  3.9  pounds  of  modified  milk  contain- 
ing 5  per  cent,  of  fat. 

Applying  these  results  to  a  specific  case,  how  much 
skim-milk  should  be  removed  from  980  pounds  of 
3.9  per  cent,  milk  to  increase  the  fat  to  5  per  cent? 
Divide  980  by  5  (B  —  C),  which  gives  196,  and  mul- 
tiply this  by  i.i  (B  —  A)  which  gives  215.6  pounds  of 
milk-serum  or  skim-milk  to  be  removed,  leaving  764.4 
pounds  of  modified  5  per  cent.  milk. 

(3)  When  the  per  cent,  of  fat  is  to  be  decreased  by 
adding  skim-milk.  Rule  —  From  the  per  cent,  of  fat 
in  the  milk  to  be  modified  subtract  the  per  cent,  of  fat 
desired  in  the  modified  milk,  and  the  result  is  the  num- 
ber of  pounds  of  skim-milk  to  be  used.  From  the  per 
cent,  of  fat  desired  in  the  modified  milk,  subtract  the 
per  cent,  of  fat  in  the  skim-milk,  and  the  result  is  the 
number  of  pounds  to  use  of  the  milk  to  be  modified. 
Example:  How  much  skim-milk  containing  .1  per 
cent  of  fat  should  be  added  to  milk  containing  5  per 
cent,  of  fat  to  reduce  the  fat  to  3.9  per  cent.? 


A—5  -         -  B—C—  3.8  (pounds  of  5  per  cent.  milk). 


C—  =.1  _  'A—  B—  i.x  (pounds  of  skim-milk). 
Skim-milk 

(a)  How  much  skim-milk  should  be  added  to  1,000 
pounds  of  5  per  cent,  milk  to  produce  3.9  per  cent. 
milk?  Divide  1,000  by  3.8,  giving  263,  and  multiply 
the  result  by  i.i,  which  gives  289,  the  number  of 


MODERN    METHODS   OF  TESTING   MILK 

pounds  of  skim-milk.     There  would  be  1,289  pounds 
of  3.9  per  cent.  milk. 

(b)  How  much  skim-milk  is  needed  to  produce 
1,000  pounds  of  modified  3.9  per  cent,  milk?  Divide 
1,000  by  4.9,  which  gives  204.08.  This,  multiplied  by 
3.8,  gives  775.5  pounds  of  5  per  cent,  milk  to  use  and, 
multiplied  by  i.i,  gives  224.5  pounds  of  skim-milk. 

EXAMPLES  FOR  PRACTICE 

(1)  What  amount  of  milk  containing  4.7  per  cent 
of  fat,  and  of  cream  containing  30  per  cent,  of  fat, 
should  be  mixed  in  order  to  produce  740  pounds  of 
milk  containing  6  per  cent,  of  fat? 

(2)  Mix  milk  containing  5.2  per  cent,  of  fat  with 
milk  containing  3.3  per  cent  of  fat  in  such  amounts 
as  to  produce  956  pounds  of  milk  containing  4.1  per 
cent,  of  fat. 

(3)  How  many  pounds  of  separator  skim-milk  must 
be  mixed  with   100  pounds  of  cream  containing  20 
per  cent,  of  fat  in  order  to  produce  a  modified  milk 
containing  5  per  cent,  of  fat? 

(4)  How  many  pounds  of  skim-milk  must  be  mixed 
with  two  pounds  of  4.5  per  cent,  milk  in  order  to  pro- 
duce a  mixture  containing  3  per  cent,  of  fat? 

(5)  How  much  skim-milk  must  be  removed  from 
milk  containing  3  per  cent,  of  fat  in  order  to  increase 
the  fat  to  3.7  per  cent.? 

15.   CORRECTING   QUEVENNE   LACTOMETER 
READING  FOR  TEMPERATURE 

Rule. — For  each  degree  F.  above  60°  F.  add  .1,  and 
for  each  degree  below  60°  F.  subtract  .1  (See  p.  181 ). 


ARITHMETIC   OF   MILK  AND   MILK   PRODUCTS     269 

16.  CONVERTING  QUEVENNE  INTO  BOARD  OF 
HEALTH  LACTOMETER  DEGREES 

Rule. — Divide  the  Quevenne  reading  by  .29.  (See 
p.  182.) 

17.  CONVERTING  BOARp   OF  HEALTH  INTO 
QUEVENNE  LACTOMETER  DEGREES 

Rule. — Multiply  the  Board  of  Health  reading  by 
.29.  (See  p.  182. ) 

18.    CORRECTING  BOARD  OF  HEALTH  LACTOM- 
ETER READING  FOR  TEMPERATURE 

Rule. — For  each  degree  F.  of  temperature  above 
60°  F.  add  .3,  and  for  each  degree  below  60°  F.  sub- 
tract .3.  (See  p.  184.) 

19.  CHANGING  VOLUME  INTO  WEIGHT 

Rule. — To  convert  a  known  volume  of  a  liquid 
into  pounds  when  the  specific  gravity  is  known,  mul- 
tiply the  specific  gravity  of  the  liquid  by  the  weight 
of  an  equal  volume  of  water.  Example :  One  gallon  of 
water  weighs  8.33  pounds;  what  is  the  weight  of  a 
gallon  of  milk  whose  specific  gravity  is  1.032?  Mul- 
tiplying 8.33  by  1,032,  we  have  as  the  answer  8.6 
pounds. 

20.  CHANGING  POUNDS  OF  MILK  INTO  QUARTS 

Rule. — Divide  the  number  of  pounds  of  milk  by  2.15. 
Example:  How  many  quarts  of  milk  in  100  pounds? 
iocH-2i5.:=46.5  quarts. 


27O  MODERN    METHODS  OF  TESTING   MILK 

21.  CHANGING  QUARTS  OF  MILK  INTO  POUNDS 

Rule. — Multiply  the  number  of  quarts  by  2.15.  Ex- 
ample :  How  many  pounds  in  40  quarts  of  milk  ?  40 
X2.i5=86  pounds. 


22.  CHANGING  DEGREES  FAHRENHEIT  INTO 
DEGREES  CENTIGRADE 

Rule.  —  From  the  degrees  F.  subtract  32  and  mul- 
tiply the  result  by  5-9.  Example:  162°  F.=(i62  —  32) 
x5-9=72°  C. 


23.  CHANGING  DEGREES  CENTIGRADE  INTO 
DEGREES  FAHRENHEIT 

Rule.  —  Multiply  the  degrees  C.  by  9-5  and  add  32. 
Example:  72°  C.=  (72X9-5)+32=i62°  F. 


24.  FINDING  THE  TRUE  AVERAGE 

Rule. — To  find  the  true  average  per  cent,  of  fat  in 
different  lots  of  milk  or  milk  products,  Und  the  weight 
of  fat  in  each  separate  lot  by  Rule  i,  add  these  amounts 
and  divide  the  sum  by  the  total  weight  of  milk  or  milk 
products.  Example:  What  is  the  average  per  cent, 
of  fat  in  the  following  lots  of  milk  ? 

Pounds  Per  cent*  Pounds 

of  milk  of  fat  of  fat 

400  containing  4.3 17.2 

300  34 io.2l 

800  5.2 41.6 

100  3.1 3-i 


i, 600 


ARITHMETIC  OF   MILK  AND   MILK   PRODUCTS      271 

Applying  Rule  I,  we  find  the  weight  of  fat  in  each 
lot  of  milk,  the  results  being  indicated  in  the  third 
column  above.  The  total  amount  of  fat  in  all  of  the 
milks  is  72.1  pounds,  which,  divided  by  1,600  (the 
total  weight  of  milk),  gives  4.5  as  the  real  average 
per  cent,  of  fat  in  all  the  milk. 

It  is  wrong  to  regard  as  the  average  per  cent,  the 
result  obtained  by  adding  the  per  cents,  directly  and 
then  dividing  this  sum  by  the  number  of  lots  repre- 
sented, unless  the  amounts  of  milk  or  milk  products 
are  equal.  Thus,  in  the  foregoing  example,  the  result 
of  such  a  wrong  method  would  make  the  average  4 
per  cent.,  when  it  is  really  4.5. 

The  same  principle  explains  why  we  do  not  get  a 
true  average  composite  sample,  when  we  take  the 
same  amount  of  milk  from  different  lots  that  vary 
considerably  in  weight  and  per  cent,  of  fat. 

EXAMPLES  FOR  PRACTICE 

1 i )  Find  the  average  per  cent,  of  fat  in  the  follow- 
ing lots  of  milk:     1,200  pounds,  3  per  cent,  of  fat; 
2,000  pounds,  5  per  cent,  of  fat;  6,000  pounds,  4  per 
cent,  of  fat;  and  1,800  pounds,  3.5  per  cent,  of  fat. 

(2)  Find  the   average  per   cent,   of   fat  in    i,ooC 
pounds  of  cream,  40  per  cent,  of  fat;  1,600  pounds,  30 
per  cent,  of  fat;  and  400  pounds,  20  per  cent,  of  fat. 

25.    FINDING  AMOUNT  OF  CREAM      .. 

Rule. — To  find  the  amount  of  cream  produced  for 
100  pounds  of  milk  when  the  per  cent,  of  fat  in  milk 
and  in  cream  is  known,  divide  the  per  cent,  of  fat  in 


272  MODERN    METHODS   OF   TESTING   MILK 

milk  by  the  per  cent,  of  fat  in  cream  and  multiply  the 
result  by  100.  Example:  How  many  pounds  of 
cream  containing  25  per  cent,  of  fat  are  produced 
from  100  pounds  of  milk  containing  5  per  cent,  of  fat? 
5-f-25=.2.  .2x100=20,  number  of  pounds  of  cream 
with  25  per  cent  of  fat. 


26.    FINDING  AMOUNT  OF  SKIM-MILK 

Rule. — To  find  the  amount  of  skim-milk  for  100 
pounds  of  milk  when  the  per  cent,  of  fat  in  milk  and 
in  cream  is  known,  find  the  amount  of  cream  by  Rule 
25  and  then  subtract  this  from  100.  Example :  How 
much  skim-milk  is  produced  from  100  pounds  of  milk 
containing  4  per  cent,  of  fat  when  the  cream  contains 
25  per  cent  of  fat?  4-^25=. 16;  .16x100=16;  100 — 
16=84,  number  of  pounds  of  skim-milk. 

27.    FINDING  AMOUNT  OF  BUTTERMILK 

Rule. — To  find  the  amount  of  buttermilk  for  100 
pounds  of  milk  when  the  per  cent,  of  fat  in  milk  and 
in  cream  is  known,  multiply  the  amount  of  fat  in  100 
pounds  of  milk  by  1.17  and  subtract  the  Result  from 
the  amount  of  cream.  Example :  How  many  pounds 
of  buttermilk  are  produced  for  100  pounds  of  milk 
containing  4  per  cent,  of  fat,  when  the  cream  used 
contains  25  per  cent,  of  fat?  4x1.17=4.68  (pounds 
of  butter  made)  ;  4-^-25x100=16  (pounds  of  25  per 
cent,  cream)  ;  16 — 4.68=11.32  (pounds  of  buttermilk). 


ARITHMETIC  OF   MILK  AND   MILK  PRODUCTS      273 

28.     FINDING  SPECIFIC  GRAVITY  OF 
MILK-SOLIDS 

Rule. — To  find  the  specific  gravity  of  milk-solids, 
when  the  specific  gravity  of  the  milk  and  per  cent,  of 
milk-solids  are  known,  multiply  the  specific  gravity  of 
the  milk  by  100,  from  the  result  subtract  100  and  di- 
vide this  result  by  the  specific  gravity  of  the  milk.  Sub- 
tract the  last  result  from  the  per  cent,  of  milk-solids 
and  then  divide  this  result  by  the  per  cent,  of  milk- 
solids.  (See  p.  187). 

29.     FINDING  AMOUNT  OF  ADDED  WATER 

IN  MILK 
See  page  201. 

30.     TABLE    SHOWING   APPROXIMATE    EQUIVA- 
LENTS OF  METRIC  SYSTEM 

1  fluid  ounce  —  29.60  cubic  centimeters   (cc.) 

1  quart  =       0.95  liter  (1) 

1  gallon  —  3.8     liters. 

1  grain  =  65.       miligrams   (mg.) 

1  ounce  (av.)  =  28.35  grams    (gm.) 

1  pound  =         .45  kilogram   (kg.) 


APPENDIX 


STANDARDS  FOR  GLASSWARE  USED  IN 
BABCOCK  TEST 

So  great  variations  were  found  in  the  forms  and  ac- 
curacy of  the  glassware  used  in  the  Babcock  test  that 
it  became  necessary  for  official  bodies  to  make  investi- 
gations and  adopt  certain  recognized  standards.  The 
Dairy  Instructors'  Association,  in  1911,  adopted 'de- 
tailed specifications  in  regard  to  the  construction  and 
graduation,  etc.,  of  such  glassware,  while  the  Associa- 
tion of  Official  Agricultural  Chemists,  in  1908,  adopted 
standards  of  accuracy  and  rules  for  testing,  as  given 
below : 


SPECIFICATIONS   FOR  CONSTRUCTION   AND 

GRADUATION  OF  STANDARD  BABCOCK 

GLASSWARE 

The  following  are  standard  Babcock  test-bottles  for 
milk  and  cream : 

(1)  Milk-test  bottles,  8  per  cent.,  i8-gram,  6-inch. 

(2)  Cream-test  bottles,  50  per  cent.,  g-gram,  6-inch. 

(3)  Cream-test  bottles,  50  per  cent.,  9-gram,  9-inch. 

Standard  milk-test  bottles:  8  per  cent.,  18-gram, 
6-inch. — (i)  Graduation — The  total  per  cent,  gradua- 
tion shall  be  8.  The  graduated  portion  of  the  neck  shall 
have  a  length  of  not  less  than  63.5  mm.  (2l/2  inches). 
The  graduation  shall  represent  whole  per  cent,  five- 
tenths  per  cent,  and  tenths  per  cent.  The  tenths  per 
cent,  graduations  shall  be  no  less  than  3  mm.  in  length ; 

275 


2/6  MODERN   METHODS  OF  TESTING  MILK 

the  five-tenths  per  cent,  graduations  shall  be  i  mm. 
longer  than  the  tenths  per  cent,  graduations,  project- 
ing i  mm.  to  the  left ;  the  whole  per  cent,  graduations 
shall  extend  one-half  way  around  the  neck  to  the  right 
and  projecting  2  mm.  to  the  left  of  the  tenths  per  cent, 
graduations.  Each  per  cent,  graduation  shall  be 
numbered,  the  number  being  placed  on  the  left  of  the 
scale.  The  error  at  any  point  of  the  scale  shall  not 
exceed  one-tenth  per  cent. 

(2)  Neck — The  neck  shall  be  cylindrical  for  at  least 
9  mm.  below  the  lowest  and  above  the  highest  gradua- 
tion mark.     The  top  of  the  neck  shall  be  flared  to  a 
diameter  of  not  less  than  10  mm. 

(3)  Bulb — The  capacity  of  the  bulb  up  to  the  junc- 
tion of  the  neck  shall  not  be  less  than  45  cc.    The  shape 
of  the  bulb  may  be  either  cylindrical  or  conical,  with 
the  smallest  diameter  at  the  bottom.    If  cylindrical,  the 
outside  diameter  shall  be  between  34  and  36  mm. ;  if 
conical,  the  outside  diameter  of  the  base  shall  be  be- 
tween 31  and  33  mm.  and  the  maximum  diameter  be- 
tween 35  and  37  mm. 

(4)  The  charge  of  the  bottle  shall  be  18  grams. 

(5)  The  total  height  of  the  bottle  shall  be  between 
150  and  165  mm.  (5^  and  6]/2  inches). 

(6)  Each  bottle  shall  bear  a  permanent  identifica- 
tion number. 

Standard  cream-test  bottles :  50  per  cent.,  9-gram, 
so-called  6-inch,  and  9-inch. — (i)  Graduation — The 
total  per  cent,  graduation  shall  be  50.  The  graduated 
portion  of  the  neck  shall  have  a  length  of  not  less  than 
63.5  mm.  (2,y2  inches).  The  graduation  shall  represent 
5  per  cent.,  i  per  cent.,  and  five-tenths  per  cent.  The 
five-tenths  per  cent,  graduations  shall  be  at  least  3  mm. 
in  length;  the  i  per  cent,  graduations  shall  be  2  mm. 
longer  than  the  five-tenths  per  cent,  graduations,  pro- 
jecting 2  mm.  to  the  left;  the  5  per  cent,  graduations 
shall  extend  halfway  around  the  neck  to  the  right  and 
project  4  mm.  to  the  left  of  the  five-tenths  per  cent. 


APPENDIX  277 

graduations.  Each  5  per  cent,  graduation  shall  be 
numbered,  the  number  being  placed  on  the  left  of  the 
scale.  The  error  at  any  point  of  the  scale  shall  not 
exceed  five-tenths  per  cent. 

(2)  Neck — (Same    as    standard    milk   test-bottle). 
The  neck  shall  be  cylindrical  for  at  least  9  mm.  below 
the  lowest  and  above  the  highest  graduation  mark.  The 
top  of  the  neck  shall  be  flared  to  a  diameter  of  not  less 
than  10  mm. 

(3)  Bulb — (Same    as    standard    milk    test-bottle). 
The  capacity  of  the  bulb  up  to  the  junction  of  the  neck 
shall  not  be  less  than  45  cc.    The  shape  of  the  bulb  may 
be  either  cylindrical  or  conical,  with  the  smallest  diam- 
eter at  the  bottom.    If  cylindrical,  the  outside  diameter 
shall  be  between  34  and  36  mm. ;  if  conical,  the  out- 
side diameter  of  the  base  shall  be  between  31  and  33 
mm.  and  the  maximum  diameter  between  35  and  37 
mm. 

(4)  The  charge  of  the  bottle  shall  be  9  grams. 

(5)  The  total  height  of  the  6-inch  bottle  shall  be 
between  150  and  165  mm.  (5%  and  6y2  inches),  (same 
as  standard  milk-test  bottles)  ;  of  9-inch  bottles,  be- 
tween 210  and  225  mm.  (8*4  and  8%  inches). 

(6)  All  bottles  shall  bear  on  top  of  the  neck,  above 
the  graduations,  in  plainly  legible  characters,  a  mark 
defining  the  weight  of  the  charge  to  be  used  (9  gram). 

Each  bottle  shall  bear  a  permanent  identification 
number. 

Standard  Pipette. — Total  length  of  pipette  not  more 
than  330  mm.  (13*4  in.). 

Outside  diameter  of  suction  tube,  6  to  8  mm. 

Length  of  suction  tube,  130  mm. 

Outside  diameter  of  delivery  tube,  4.5  to  5.5  mm. 

Length  of  delivery  tube,  100  to  120  mm. 

Distance  graduation  mark  above  bulb,  50  to  60  mm. 

Nozzle,  straight. 

Delivery,  17.6  cc.  of  water  at  20  degrees  C.  in  5  to  8 
seconds. 


278  MODERN    METHODS    OF    TESTING    MILK 

STANDARD  OF  ACCURACY  FOR  BABCOCK 
GLASSWARE  AND  RULES  FOR  TESTING 

SECTION  *. — The  unit  of  graduation  for  all  Babcock 
glassware  shall  be  the  true  cubic  centimeter  (.998877 
gram  of  water  at  4  degrees  C). 

(a)  With  bottles,  the  capacity  of  each  per  cent,  on 
the  scale  shall  be  two-tenths  (0.20)  cubic  centimeter. 

(b)  With  pipettes  and  acid  measures,  the  delivery 
shall  be  the  intent  of  the  graduation,  and  the  gradua- 
tion shall  be  read  with  the  bottom  of  the  meniscus  in 
line  with  the  mark. 

SECTION  2 — The  official  method  for  testing  bottles 
shall  be  calibration  with  mercury  (13.5471  grams  of 
clean,  dry  mercury  at  20  degrees  C.,  carefully  weighed 
on  analytical  balances,  to  be  equal  to  5  per  cent,  on  the 
Babcock  scale),  the  bottles  being  previously  filled  to 
zero  with  mercury. 

SECTION  3 — Optional  methods — The  mercury  and 
cork,  alcohol  and  burette,  and  alcohol  and  brass- 
plunger  methods  may  be  employed  for  the  rapid  testing 
of  Babcock  bottles,  but  the  accuracy  of  all  questionable 
bottles  shall  be  determined  by  the  official  method. 

SECTION  4 — The  official  method  for  testing  pipettes 
and  acid-measures  shall  be  calibration  by  measuring  in 
a  burette  the  quantity  of  water  (at  20  degrees  C.)  de- 
livered. 

SECTION  5 — The  limits  of  error — (a)  For  Babcock 
bottles  shall  be  the  smallest  graduation  on  the  scale, 
but  in  no  case  shall  it  exceed  five-tenths  (0.50)  per 
cent.,  or  for  skim-milk  bottles  one-hundredth  (o.oi) 
per  cent. 

(b)  For  full-quantity  pipettes,  it  shall  not  exceed 
one-tenth   (o.io)   cubic  centimeter,  and  for  fractional 
pipettes,  five-hundredths  (0.05)  cubic  centimeter. 

(c)  For  acid-measures  it  shall  not  exceed  two-tenths 
(0.20)  cubic  centimeter. 


INDEX 


Acid,  lactic,  from  milk-sugar   .  13 
Estimation    of        .      .      .      131-151 
Acid,  sulphuric,  action  in  Bab- 
cock  test 33 

Adding  to  milk       ....  60 

Care  in  handling  .....  45 
Effect    of    strong    and    weak 

acid 43 

Measuring    for    test    ...  60 

Mixing  with  milk        ...  62 

Strength  of       .      .      .      .     \  43 

Temperature  when  used  .      .  61 

Testing   strength   of    ...  44 

Acid-hydrometer 44 

Acid-measures        .      .      .      .     37,  38 

Testing  accuracy  of    ...  53 

Acid   solution 133 

Acid  tester 44 

Acid  tests,   Mann's    ....  145 

Spillman's 143 

Acid's,  action  on  alkalis     .      .  132 

In    milk-fat 3 

Volatile   acids      ....  4 

Acidity,  indicators  for    .      .      .  133 

In  milk,  causes  and  kinds  of  131 

In  milk  in  relation  to  bacteria  153 

In  rich  and  poor  cream   .      .  150 

Principles  of  testing   .      .      .  132 

Rapid  estimation  of    ...  144 

Testing  of,  in  cheese  .      .      .  148 

In  cream  and  milk       .      139-147 

In  whey 148 

Acidometer 44 

Adulterations  of  butter        .      .  209 

Cheese     . 210 

Cream 208 

Milk 201 


v  PAGE 

Age  of  composite  samples  when 

tested 31 

Of  milk,  testing  by  rennet   .  174 

Albumin  in  milk        ....  11 

In  relation  to  casein  ...  12 

Alcohol  test  for  acidity       .      .  153 

Alkalis,  action  on  acids       .      .  132 

Alkaline  solution        ....  133 

Alkaline-tablet   test    ....  142 
Analysis.     See  Composition. 

Annatto,   detection   of,   in   milk  207 

Apparatus  in  Babcock  test       .  32 

Testing  accuracy  of    ...  46 
Appearance      in      judging      and 

scoring   butter    ....  227 

Cheese 240 

Arithmetic  of  milk  and  products 

253-273 

Arnold  test  for   heated   milk    .  162 

Ash  in  milk 13 

Average,  true,  how  to  find        .  270 

Babcock  test 32 

Acid  measure 37 

Acid   used   in 43 

Action  of  acid        ....  33 

Apparatus 32 

Benefits  of  use        ....  32 

Bottles 34,   75,  94 

Centrifugal    machines    .      .     38-42 

For  butter 102 

For  buttermilk        ....  95 

For    cheese 109 

For  condensed  milk    ...  97 

For  cream 73 

For  milk 57 

For    milk    powder        ...  99 

For  skim-milk   .  93 


279 


280 


MODERN    METHODS   OF  TESTING   MILK 


PAGE 

Babcock  test  for  whey  ...  93 

Glassware  standards    ...  275 

Modifications    of    .      .      .      .  70 

Operation    of 57 

Pipette 35 

Principles  underlying        .      .  33 

Reading   results      ....  65 

Testers  ' 38 

Testing  accuracy  of  apparatus  46 

Use  of  centrifugal  force       .  33 

Water  used  in        ....  64 

Bacteria  and  acidity  of  milk   .  153 

Bacterial     condition     of     milk,. 

testing 152 

Barthel's   reductase   test      .      .159 
Benkendorf   moisture-test    oven  117 
Bichromate    of    potash    as    pre- 
servative    29 

Board  of  Health  lactometer      .  181 

Body   of   butter 222 

Of   cheese 236 

Boiling    test    for    acidity     .      .  153 

Borax   in   milk,   detection    of    .  208 

Bottles,    Babcock  test,  for  cream  75 

For   milk 34 

For    skim-milk,    whey,    etc.    .  94 

Butter,    appearance    in   judging  227 

Body  of 222 

Calculating    dividends    for    .  261 

Calculating  water  in   .      .      .  114 

Classes    of 230 

Color    of 224 

Commercial   testing,  judging, 

and    scoring        ....  218 

Composition  of       ....  16 

Definition    of 18 

Finish    of 227 

Flavor    of 219 

Grades   of          231 

Judging 218 

Moisture  in  testing   .      .      110-124 

"Overrun,"  how  to  calculate  256 

Package 227 

Qualities    of 219 

Renovated        ....      18,  209 

Salt    in,    judging    ....  226 


PAGE 

Salt  in,  testing       ....  125 

Sampling  for   fat-test        .      .  101 

For  judging  and  scoring       .  218 

Scale    of    points    ....  228 

Score-cards 228 

Scoring         227 

Shaw  test  for  fat  in              .  103 

Standard    of 18 

Tests  for  salt  in   .      .      .      .  125 
Tests  for  water  in     .      .      110-124 

Texture   of 221 

Yield  of,  how  to  calculate   .  257 

Butter-fat.      See   Milk-fat. 

Buttermilk,  composition  of        .  16 

Testing  fat   in        ....  93 

Yield    of,   calculating        .      .  272 

Butter-trier 219 

Butyrometer,   Gerber's    ...  71 
By-products    of    milk,    composi- 
tion   of 16 

Calcium    casein 9 

Calibration    of    glassware    .      .  46 

Casein  in  milk,  action  of  acids  9 

Of   alkalis 10 

.   Of   heat 10 

Of   rennet    ......  10 

Tests   for      ....      189-200 

Calculating  amount  of,   from 

fat  in   milk 260 

Composition    of      ....  9 

Compounds 10 

Per  cent,  in  milk  ....  12 

Products  formed  from      .      .  11 

Proportion    to    albumin    .      .  12 

Catalase    tests        ....  160 
Centigrade    degrees    calculating 

to    Fahrenheit    ....  270 
Centrifugal    force    in    Babcock 

test 33 

Machines 38 

Centrifuges   .      .      .      .      39,  41,   166 
Cheddar       cheese,       American, 

composition   of    .      .      .      .  16 
Commercial   testing,   judging, 

and    scoring     .      .      .      218,  233 

Cheese,   adulterations  of      .      .  210 


INDEX 


28l 


PAGE 

Appearance  and  finish  of     .  240 

Body  of 236 

Calculating  yield  of,  from  fat  259 
From   fat   and   casein    .      259,   261 

Classes   of 241 

Color    of      .  ' 238 

Commercial  judging,   testing, 

and  scoring  of      .      .      218,   233 

Commercial   qualities    of        .  233 

Composition    of      ....  16 

Definition    of 19 

Dividends    from,    calculating  263 

Finish    of 240 

Flavor    of 233 

Judging   of 233 

Package 240 

Salt    in 239 

Sampling  for  fat-testing        .  108 

For  judging  and  scoring   .  233 

Score-cards 241 

Scoring 241 

Standard 19 

Testing  acidity  in        ...  148 

Testing  commercial    qualities  233 

Testing  fat   in        ....  109 

Testing  acid  in      ....  148 

Texture 235 

Trier    for    sampling    .      .      .  233 
Yield  of,  calculating        .      258-261 
Cheese-factory,  calculating  divi- 
dends  of 263 

Chemistry   of   cow's   milk    .      .  1 

Churned  samples  of  milk   .      .  21 

Prevention    of         ....  22 

Sampling    of 21 

Cleaning  greasy  glassware        .  53 
Collecting   sediment   in   milk    .  163 
Coloring  matter  in  milk,  detec- 
tion   of 207 

Commercial     testing,     judging, 

and  scoring  of  butter  .      .  218 

Of  certified  milk   ....  250 

Of   cheese 233 

Of    cream 250 

Of  milk 247 

Of  standardized  milk       .      .  250 


PAGE 

Composite   samples,  age  for  test- 
ing         31 

Care   of 30 

Description 24 

Method   of  taking        ...  26 

Preserving          28 

Sampling  for  test       ...  58 

Sample-jars 25 

Composition    of    butter         .      .  16 

Buttermilk         16 

Casein 9 

Composition  of  cheese    ...  16 

Milk IS 

Milk-fat 3 

Skim-milk 16 

Whey 16 

Condensed  milk,  testing  fat  of  97 
Cornell  test  for  water  in  butter  115 
Corrosive    sublimate    as    pre- 
servative           28 

Cows,   testing  on    farm        .      .  211 

Cow's    milk,    analyses    of    .      .  15 

Chemistry    of 1 

Composition    of      ....  15 

Definition    of 16 

Standard  of 16 

Cream,  acidity  of,  testing   .      .  141 

Adulterations   of    ....  208 

Bottles,   bulb-necked    ...  77 

Straight-necked         ...  75 

Calculating  yield  of    .      .      .  271 

Color  of  fat-column    ...  68 
Commercial    testing,    scoring 

and  judging        ....  250 

Definition    of    .  •  .      .      .      .  18 

Keeping   samples   of    ...  84 

Method  of  sampling   ...  82 

Poor  and  rich,  acidity  in      .  149 

Preparing  sample  for  testing  85 

Standard 18 

Testing   fat   in    .      .      .      .      73-92 

Weighing  sample  of   ...  87 

Cream  scales 79,  80 

Creamery  dividends,  calculation 

of 261 

Curd-test,    Wisconsin      .      .      .  155 


282 


MODERN    METHODS   OF  TESTING    MILK 


PAGE 

Cylinder,  for  lactometer     .      .  181 

Spillman's,   acid-test    .      .      .  144 

Dean  moisture-test  oven      .      .  119 
Definitions    of    milk    and    milk 

products      .      .      .      .      .     16-19 

Detection    in    milk,    of   annatto  207 

Borax 208 

Coloring    matter    ....  207 

Formalin 207 

Of  skimmed  milk     .      .      204,  206 
Of  watered  milk        .      .      201,  206 
Dipper,    sampling      ....  27 
Dirt  in  milk,  testing       .      .      .  163 
Dividends,  calculating,  at  cream- 
eries      261 

At   cheese-factories      .      .      .  263 

Double-necked  test-bottles   .      .  94 

Draining-rack 54 

Enzyms   in  milk,  tests   for        .  158 

Farrington    moisture-test    oven  117 

Farm,  testing  milk  on   .      .      .  211 

Farrington's  alkaline-tablet  test  142 

Bottle-cleaner 55 

Fat  in  milk.     See  milk-fat. 

Fat-column,  black  particles  in  .  68 

Gas-bubbles   in        ....  69 

Measuring,    in    cream-testing  90 

White  particles  in       ...  69 

Fat-globules,    in    milk,    number  4 

Size 4 

Influences    affecting    ...  5 

In  cheese,  etc 5 

Fermentation     test      of     milk, 

Wisconsin 155 

Gerber's        ..*....  158 

Finish  of  butter 227 

Of   cheese 240 

Flavor  of  butter       .      .      .      .  219 

Cheese 233 

Milk,    cream,   etc.        .      .      .  245 
Formalin  in  milk,   as  preserva- 
tive        29 

Detection    of     .      .      .      .      .207 

Frozen  milk,  sampling  of   .      .  23 

Gerber's    butyrometer     ...  71 

I  ermentation   test        .      .      .  158 


PAGE 

"Sal"  test 72 

Glassware     in     Babcock     test, 

calibration    of     ....       46 

Cleaning    of 53 

Testing  accuracy  of  ...  46 
Globulin  in  milk  ....  11 
Glycerin  in  milk-fat  ...  3 
Grades  of  butter  .  .  .  .231 

Of   cheese 241 

Guaiac  test  for  heated  milk  .  162 
Hand-testers  .  .  .  .  40,  166 
Heated  milk,  tests  for  .  161-163 
Hydrometer  for  testing  specific 

gravity 178 

Testing  strength  of  acid  .  44 
Ice-cream,  tests  for  ...  95 
Indicator  in  testing  acidity  .  133 
Irish  test  for  water  in  butter  119 
Jars,  waste,  for  emptying  test- 
bottles  53 

Jars,  for  composite  samples  .  25 
Jensen's  reduction-fermentation 

test 159 

Judging  butter    ....     218-227 

Cheese         233-241 

Cream     .      .      .      .      .      .      .250 

Milk 242-250 

Kumiss,  definition  of      ...        19 

Lactic  acid  and  casein   ...          9 

Lactic  acid  in  milk  .      .      .      13,  131 

Estimation   of        ...     139-148 

From  milk  sugar   ....        13 

Lactose 13 

Lactometer,  application  .  177-187 
Board  of  Health  ....  181 
Bi-chromate,  effect  on  .  .  184 

*,^£Xrlinder    for 181 

MfciJ^^  using          .      .      .      179 

Quevenne 178 

Temperature,  effect  on  177,  179 
Lorenz  dirt-tester  ....  165 
Mann's  acid  test  ....  145 
Marschall  acid  test  .  .  .  145 
Marschall  rennet  test  .  .  .  171 
Measures  for  acid  ....  36 
Measuring,  acid 60 


INDEX 


283 


PAGE 

Fat-column   in  testing  cream  90 

In   testing  milk        ...  65 
Methylene-blue  test   for  heated 

milk 163 

Metric"  system,    equivalents    of  273 

Milk,  acidity  of 131 

Adding    acid    to     ....  60 

Adulteration     of     ....  201 
Age  of,  testing       .      153,  158,  174 

Albumin  in 11 

Analyses  of 15 

Arithmetic  of 253 

Ash   in 13 

Chemistry    of 1 

Churned,   sampling  of  21 

Color  of 246 

Certified,   judging        ...  250 

Composite    sampling   of    .      .  24 

Composition     of     ....  15 

Condensed 17,   97 

Definition    of 16 

Detection  of  adulterations  in  201 

Enzyms,    tests    for      .      .      .  158 

Flavor   of 245 

Frozen,  sampling  of   ...  23 

Gases  in 14 

Judging  and   scoring        .      .  247 

Keeping  power  of       ...  244 

Mixing  with  acid  ....  62 

Modified,  to  prepare   .      .      .  263 

Nitrogen,  compounds  of        .  8 

Salts  in 13 

Sampling  of 20-31 

Sampling  with   pipette     .      .  58 

Scale  of  points  in  judging   .  247 

Scoring  of 247 

Skimmed,  detection  of  .     204,  206 

Sour,    sampling   of      ...  23 

Souring   of 13 

Specific   gravity   of      .      .      .  175 

Standard    of 17 

Standardized,  to  prepare       .  263 
Standardized,     judging     and 

scoring 250 

Temperature  for  testing        .  61 


PAGE 

Terms    used   in   judging   and 

scoring 242 

Testing  acidity  of  .  .  131-148 
Testing  sanitary  condition  of  152 
Total  solids  of  ...  3,  185 
Watered,  detection  of  .  201,  206 

Milk-albumin         11 

Milk-bottle,    use    of    in    cream- 
testing       73 

Milk,    Casein.      See   Casein. 
Milk-fat,    color    of   in    Babcock 

test      . 68 

•Composition  of  .      .      .      .         3 

Definition    of 18 

Glycerin   in        4 

Influenced  by  various  condi- 
tions           5-8 

In  relation  to  butter  yield  .  257 
In  relation  to  casein  .  .  260 
In  relation  to  cheese  .  .  258 
Method  of  testing,  in  butter 

102-108 
In  buttermilk      ....        93 

In    cheese 109 

In  condensed  milk  ...        97 

In   cream 73-92 

In  milk 57-72 

In  milk   powders     ...        99 
In    skim-milk      ....       93 

In  whey 93 

Per  cent,  in  foremilk  .  .  8 
In  strippings  ...  8 
Standard  of  ....  18 
Variation  of,  in  milk  .  .  5 
Volatile  acids  in  ...  4 

Milk-globulin         11 

Milk,  measuring  with  pipette   .        58 

Milk  powders,   testing  of    .      .       99 

Milk  products,  arithmetic  of   .     253 

Composition    of      ....        16 

Judging  and  scoring       .     242-250 

Milk    serum 15 

Milk-solids,  composition  of  .  3,  14 
Estimating  by  lactometer  .  185 
Specific  gravity  of  .  .  .  175 
Milk-sugar 13 


284 


MODERN    METHODS   OF   TESTING   MILK 


Milk   testing,   Babcock  test    .     32-57 

On   the   farm 211 

Mixing  milk  and  acid    ...  62 
Moisture.      See   water. 

Monrad  rennet-test   ....  169 

Neutral    solutions      ....  133 

Neutralization 132 

Nitrogen  compounds  of  milk   .  8 

In  relation  to  fat       .      .      12,  204 
New    York    Board    of    Health 

lactometer 181 

Oleomargarin,  test  for   .      .      .  209 
"Overrun"    in    butter,    how    to 

find 256 

Package,    judging    and    scoring 

of,  in  butter       ....  227 

In    cheese 240 

Paraphenylene-diamins  test  for 

heated  milk 161 

Patrick  test  for  water  in  butter  119 
Per  cent,  of  any  constituent  of 
milk  and  products,  how  to 

find 254 

Percentages,    average,    how    to 

find 270 

Perkins  test  for  salt  in  butter  127 

Phenolphthalein  as  indicator    .  133 

Pipette,    in    Babcock   test    .  35 

Accuracy  of,  testing  ...  52 

Correct  way  to  use    ...  58 

In  cream  testing   ....  86 

Sampling  milk  with    ...  58 

Wagner's 36 

Potassium-bichromate      ...  29 

Pounds,  to  change  to  quarts   .  269 

Powdered  milk,  testing  of  .      .  99 
Preservatives      for      composite 

samples 28 

Detection  of,  in  milk        .      .  207 

Publow  acid  test        ....  145 

Qualities,  commercial,  of  butter  219 

Cheese 233 

Milk 242 

Cream .250 

Quarts  to  change  to  pounds    .  270 


PAGE 

Quevenne    lactometer,    descrip- 
tion of 178 

Correcting  for  temperature  .  179 

How  to  use 179 

Compared     with     Board     of 

Health  lactometer    .      .      .  183 

Rack,    draining   for   test-bottles  54 

For   composite    samples    .      .  26 

Reductase   tests 158 

Reduction-fermentation    test     .  159 

Rennet-test,    Marschall's      .      .  171 

Rennet-test,    Monrad's    .      .      .  169 

Renovated  butter,  definition  of  18 

How    to    detect     ....  209 

Standard  of 19 

Richmond's  slide-rule   for  find- 
ing milk-solids    ....  186 
Russian    test    for    fat    in    milk 

and    products      ....  70 
"Sal"  test  for  fat  in  milk,  etc., 

Gerber's 72 

Salt  in  butter,  commercial  judg- 
ing and  scoring        .      .      .  226 

In    cheese 239 

Tests    for     ....      125-130 

Salts  in  milk 13 

Samples.   See  Composite  samples. 

Sampling  butter     .      .      .      101,  218 

Cheese 108,  233 

Cream 79 

Milk,   composite      ....  24 

Frozen 23 

Partially   churned    ...  21 

Partially   creamed    ...  20 

Sour 23 

With  pipette       ....  58 

Sampling-dipper 27 

Sampling-tubes 27 

Sanitary     condition     of     milk, 

tests  for        ....     152-168 
Scales     for     weighing     cheese, 

cream,    etc 79,    80 

Schardinger's    test    for    heated 

milk 163 

Score-cards  for  butter    .      .      .  228 

Cheese 248 


INDEX 


285 


Scoring  butter 227 

Cheese 241 

Cream 250 

Milk 247 

Standardized  milk              .      .  250 

Sediment  in  milk,   how  to  test 

for 163 

Serum    of   milk 15 

Solids    of 15 

Shaw  test  for  fat  in  butter      .  103 

for   salt  in  butter        .      .      .  129 

Sinacid  test  for  fat  in  milk,  etc.  72 

Skim-milk,  composition  of   .  16 

Detection  of  ....     204,  206 

How  to  calculate  yield  of    .  272 

Test-bottles 94 

Testing  for  fat  in       ...  93 

Slide-rule,   Richmond's  for  cal- 
culating  solids    ....  186 

Sodium  carbonate  in  milk,   de- 
tection   of 208 

Solids-not-fat  in  milk     .      .      .  15 

How  to  find  amount  of   .      .  185 

Solids,  total,  in  milk.   See  Milk- 
solids. 

Sour  milk,  cause  of       ...  13 

Sampling   of 23 

Specific   gravity   of  milk      .      .  175 

Cylinder 181 

Effect  of   fat  on    .      .      .      .  176 

Effect  of  temperature  on      .  177 
Effect  of  water  on            .      .176 

How    to    find 17? 

Specific  gravity,  of  milk  solids  187 
Table  for  temperature  correc- 
tion     .......  180 

Speed  of  testers        ....  41 

Spillman's   acid-test   cylinder    .  144 

Standard  of  butter   ....  18 

Butter-fat 18 

Cheese 19 

Condensed    milk    ....  17 

Cream 18 

Milk-fat 18 

Standard   of   Renovated  butter  19 


PAGE 

Skim-milk 17 

Standards       for       Babcock-test 

glassware 275 

Steam-turbine  tester        ...  39 

Storch  test  for  heated  milk      .  161 

Sugar  of  milk 13 

Sulphuric  acid.     See  acid. 

Sweetened  condensed  milk       .  17 

Table  of  correction  of  specific 

gravity  for  temperatures    .  180 
Equivalents  of  metric  systems  273 
Of     degrees     of     Board     of 
Health  and  Quevenne  lac- 
tometers     183 

Temperature  of  acid  in  testing 

milk 61 

Of   fat-column   when    read    .  66 

In  relation  to  specific  gravity  177 

Of  milk  when  tested  ...  60 

Terms     describing     commercial 

qualities  of  butter   .      .      .  219 

Of   cheese 233 

Of  cream  and  milk    .      .      .  242 

Test,    Babcock.       See    Babcock 

Test. 

Curd,   Wisconsin    ....  155 

Fermentation,    Gerber's    .      .  158 

Rennet,  Marschall       .      .      .  171 

Monrad 169 

"Sal,"    Gerber's     ....  72 

Russian 70 

Sinacid         72 

Test-bottles,    accuracy   of,    test- 
ing         46 

Bulb-necked,    cream    ...  77 

Calibration         46 

Cleaning 53 

Cream 75-77 

Double-necked         ....  94 

Drain-rack 54 

Test,  Milk 34 

Rinser 54 

Skim-milk 93 

Straight-necked    cream     .      .  75 

Tester 38 

Whirling 63 


286 


MODERN    METHODS   OF   TESTING    MILK 


PAGE 

Testers,  Babcock       ....  38 

Bottle      .......  49 

Electrical     ......  41 

Estimating  speed  of    ...  41 

Hand       ......      '.  40 

Steam-turbine    .....  39 

Testing,  accuracy  of  test  bottles, 

etc  ........  46 

Acidity  of  cream,  milk,  etc.  131-151 

Age  of  milk   .      .      .      .      153,  174 

Butter        .....      102,  103 

Cheese     .      .      .....  109 

Condensed   milk     ....  97 

Cows  on  farm  .....  211 

Dirt    in    milk    .....  163 

Milk  powders   .....  99 

Pepsin     .....      .      .  174 

Rennet    .......  169 

Texture,  commercial,  of  butter  221 

Of   cheese    ......  235 

Titration     .......  135 

Total  solids  of  milk.     See  milk- 

solids. 

Trier  for  testing  butter        .      .  219 

Cheese    .......  233 

Tube,    sampling    .....  27 

Turbine    testers    .....  39 

Van  Norman  acid  test   .      .      .  141 

Volatile  acids  in   milk-fat    .      .  4 
Volume  of  liquid,   changing  to 

weight       ......  269 

Waste-acid   jar     .....  53 


Water  in  butter,  tests  for  .     110-124 

In  milk,   amount  of    ...  1 

Causes  of   variation    ...  2 

Detection    of,    in   adulterated  201 

In   butter-testing    ....  110 

In    commercial    testing    and 

judging  of  butter    .      .      .  223 
In  milk  and  milk  products     15,  16 

Used  in  Babcock  test       .      .  64 

Watered    milk,    detection    of    .  201 

Weighing   samples    of   cream    .  87 
Weight    of   any   constituent   of 
milk  and  products,  how  to 

find      .......  253 

Changing  to  volume    .      .      .  269 
Weights  and  measures,  equiva- 

lents  of  metric  system        .  273 

Whey,   composition   of    .      .      .  16 

Definition    of    .....  19 

Testing  of   ......  81 

Whirling  test-bottles       ...  59 

Wisconsin  curd-test  .      .      .      .  155 

Tests   for   water   in  butter    .  117 
Yield  of  butter,   how  to  calcu- 

late      .......  257 

Buttermilk   ......  ; 

Cheese,   for   fat      ....  258 

Cheese,  from  fat   .      .      .      .  259 

Cheese,   from  fat  and  casein 

259-2*61 

Cream  ........  271 

Skim-milk     ......  272 


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First  Principles  of  Soil  Fertility 

By  ALFRED  VIVIAN.  There  is  no  subject  of  more  vital 
importance  to  the  farmer  than  that  of  the  best  method 
of  maintaining  the  fertility  of  the  soil.  The  very  evident 
decrease  in  the  fertility  of  those  soils  which  have  been 
under  cultivation  for  a  number  of  years,  combined  with 
the  increased  competition  and  the  advanced  price  of  labor, 
have  convinced  the  intelligent  farmer  that  the  agriculture 
of  the  future  must  be  based  upon  more  rational  practices 
than  those  which  have  been  followed  in  the  past.  We 
have  felt  for  some  time  that  there  was  a  place  for  a 
brief,  and  at  the  same  time  comprehensive,  treatise  on 
this  important  subject  of  Soil  Fertility.  Professor  Vivian's 
experience  as  a  teacher  in  the  short  winter  courses  has 
admirably  fitted  him  to  present  this  matter  in  a  popular 
style.  In  this  little  book  he  has  given  the  gist  of  the 
subject  in  plain  language,  practically  devoid  of  technical 
and  scientific  terms.  It  is  pre-enr.iently  a  "First  Book," 
and  will  be  found  especially  valuable  to  those  who  desire 
an  introduction  to  the  subject,  and  who  intend  to  do  subse- 
quent reading.  Illustrated.  5x7  inches.  265  pages.  Cloth. 

The  Study  of  Corn 

By  PROF.  V.  M.  SHOESMITH.  A  most  helpful  book  to  all 
farmers  and  students  interested  in  the  selection  and  im- 
provement of  corn.  It  is  profusely  illustrated  from  photo- 
graphs, all  of  which  carry  their  own  story  anJ  contribute 
their  part  in  making  pictures  and  text  matter  a  clear,  con- 
cise and  interesting  study  of  corn.  Illustrated.  5x7  inches, 
loo  pages.  Clothe  ,,...«••..• 


Ths  Management  and  Feeding  of  Cattle 

By  PROF.  THOMAS  SHAW.  The  place  for  this  book  will 
be  at  once  apparent  when  it  is  stated  that  it  is  the  first 
book  that  has  ever  been  written  which  discusses  the  man- 
agement and  feeding  of  cattle,  from  the  birth  of  the  calf 
until  it  has  fulfilled  its  mission  in  life,  whether  on  the 
block  or  at  the  pail.  The  book  is  handsomely  printed  on 
fine  paper,  from  large,  clear  type.  Fully  illustrated.  5^x8 
inches.  496  pages.  Cloth 

The  Farmer's  Veterinarian 

By  CHARLES  WILLIAM  BURKETT.  This  book  abounds  in 
helpful  suggestions  and  valuable  information  for  the  most 
successful  treatment  of  ills  and  accidents,  and  disease 
troubles.  A  practical  treatise  on  the  diseases  of  farm 
stock;  containing  brief  and  popular  advice  on  the  nature, 
cause  and  treatment  of  disease,  the  common  ailments  and 
the  care  and  management  of  stock  when  sick.  It  is 
profusely  illustrated,  containing  a  number  of  halftone 
illustrations,  and  a  great  many  drawings  picturing  diseases, 
their  symptoms  and  familiar  attitudes  assumed  by  farm 
animals  when  affected  with  disease,  and  presents,  for  the 
first  time,  a  plain,  practical  and  satisfactory  guide  for 
farmers  who  are  interested  in  the  common  diseases  of  the 
farm.  Illustrated.  5x7  inches.  288  pages.  Cloth. 

First  Lessons  in  Dairying 

By  HUBERT  E.  VAN  NORMAN.  This  splendid  little  book 
has  been  written  from  a  practical  point  of  view,  to  fill 
a  place  in  dairy  literature  long  needed.  It  is  designed 
primarily  as  a  .practical  guide  to  successful  dairying,  an 
elementary  text-book  for  colleges  and  for  use  especially 
in  short-course  classes.  It  embodies  underlying  principles 
involved  in  the  handling  of  milk,  delivery  to  factory,  ship- 
ping station,  and  the  manufacture  of  butter  on  the  farm. 
It  is  written  in  a  simple,  popular  way,  being  free  from  tech- 
nical terms,  and  is  easily  understood  by  the  average  farm 
boy.  The  book  is  just  the  thing  for  the  every-day  dairy- 
man, and  should  be  in  the  hands  of  every  farmer  in  the 
country.  Illustrated.  5x7  inches.  100  pages.  Cloth. 

A  Dairy  Laboratory  Guide 

By  H.  E.  Ross.  While  the  book  is  intended  primarily 
for  use  in  the  laboratory,  it  should  be  of  value  to  the 
practical  dairyman.  The  time  has  come  when  the  suc- 
cessful dairyman  must  study  his  business  from  a  purely 
scientific  point  of  view,  and  in  this  book  the  scientific 
principles,  upon  which  dairy  industry  is  based,  are  stated 
clearly  and  simply,  and  wherever  it  is  possible,  these  prin- 
ciples are  illustrated  by  practical  problems  and  examoles. 

90  pa^es.     5x7  inches.     Cloth.    . 

(2) 


Profitable  Stock  Raising 

By  CLARENCE  A.  SHAMEL.  This  book  covers  fully  the 
principles  of  breeding  and  feeding  for  both  fat  stock  and 
dairying  type.  It  tells  of  sheep  and  mutton  raising,  hot 
house  lambs,  the  swine  industry  and  the  horse  market. 
Finally,  he  tells  of  the  preparation  of  stock  for  the  market 
.ind  how  to  prepare  it  so  that  it  will  bring  a  high  market 
price.  Live  stock  is  the  most  important  feature  of  farm 
life,  and  statistics  show  a  production  far  short  of  the 
actual  requirements.  There  are  many  problems  to  be 
faced  in  the  profitable  production  of  stock,  and  these  are 
fully  and  comprehensively  covered  in  Mr.  Shamel's  new 
book.  Illustrated.  5x7  inches.  288  pages.  Cloth. 


The  Business  of  Dairying 

By  C.  B.  LANE.  The  author  of  this  practical  little  book 
is  to  be  congratulated  on  the  successful  manner  in  which 
he  has  treated  so  important  a  subject.  It  has  been  pre- 
pared for  the  use  of  dairy  students,  producers  and  handlers 
of  milk,  and  all  who  make  dairying  a  business.  Its  pur- 
pose is  to  present  in  a  clear  and  concise  manner  various 
business  methods  and  systems  which  will  help  the  dairy- 
man to  reap  greater  profits.  This  book  meets  the  needs 
of  the  average  dairy  farmer,  and  if  carefully  followed  will 
lead  to  successful  dairying.  It  may  also  be  used  as  an 
elementary  textbook  for  colleges,  and  especially  in  short- 
course  classes.  Illustrated.  5x7  inches.  300  pages.  Cloth. 


Questions  and  Answers  on  Buttermaking 

By  CHAS  A.  PUBLOW.  This  book  is  entirely  different 
from  the  usual  type  of  dairy  books,  and  is  undoubtedly  in 
a  class  by  itself.  The  entire  subject  of  butter-making  in 
all  its  branches  has  been  most  thoroughly  treated,  and 
many  new  and  important  features  have  been  added.  The 
tests  for  moisture,  salt  and  acid  have  received  special 
attention,  as  have  also  the  questions  on  cream  separa- 
tion, pasteurization,  commercial  starters,  cream  ripening, 
cream  overrun,  marketing  of  butter,  and  creamery  man- 
agement. Illustrated.  5x7  inches.  100  pages  Cloth. 

Questions  and  Answers  on  Milk  and  Milk  Testing 

By  CHAS.  A.  PUBLOW,  and  HUGH  C.  TROY.  A  book  that 
no  student  in  the  dairy  industry  can  afford  to  be  without. 
No  other  treatise  of  its  kind  is  available,  and  no  book  of 
its  size  gives  so  much  practical  and  useful  information  in 
the  study  of  milk  and  milk  products.  Illustrated.  5x7 
inches.  100  pages.  Cloth 

(3? 


Soils 

By  CHARLES  WILLIAM  BURKETT,  Director  Kansas  Agri- 
cultural Experiment  Station.  The  most  complete  and 
popular  work  of  the  kind  ever  published.  As  a  rule,  a 
book  of  this  sort  is  dry  and  uninteresting,  but  in  this  case 
it  reads  like  a  novel.  The  author  has  put  into  it  his  in- 
dividuality. The  story  of  the  properties  of  the  soils,  their 
improvement  and  management,  as  well  as  a  discussion  of 
the  problems  of  crop  growing  and  crop  feeding,  make  this 
book  equally  valuable  to  the  farmer,  student  and  teacher 
Illustrated.  303  pages.  5^x8  inches.  Cloth.  . 

Weeds  of  the  Farm  Garden 

By  L.  H.  PAMMEL.  The  enormous  losses,  amounting 
to  several  hundred  million  dollars  annually  in  the  United 
States,  caused  by  weeds  stimulate  us  to  adopt  a  better 
system  of  agriculture.  The  weed  question  is,  therefore, 
a  most  important  and  vital  one  for  American  farmers. 
This  treatise  will  enable  the  farmer  to  treat  his  field  to 
remove  weeds.  The  book  is  profusely  illustrated  by  photo- 
graphs and  drawings  made  expressly  for  this  work,  and 
will  prove  invaluable  to  every  farmer,  land  owner,  gar- 
dener and  park  superintendent.  5x7  inches.  300  pages. 
Cloth 

Farm  Machinery  and  Farm  Motors 

By  J.  B.  DAVIDSON  and  L.  W.  CHASE.  Farm  Machinery 
and  Farm  Motors  is  the  first  American  book  published 
on  the  subject  of  Farm  Machinery  since  that  written  by 
J.  J.  Thomas  in  1867.  This  was  before  the  development 
of  many  of  the  more  important  farm  machines,  and  the 
general  application  of  power  to  the  work  of  the  farm. 
Modern  farm  machinery  is  indispensable  in  present-day 
farming  operations,  and  a  practical  book  like  Farm  Ma- 
chinery and  Farm  Motors  will  fill  a  much-felt  need.  The 
book  has  been  written  from  lectures  used  by  the  authors 
before  their  classes  for  several  years,  and  which  were  pre- 
pared from  practical  experience  and  a  thorough  review  of 
the  literature  pertaining  to  the  subject.  Although  written 
primarily  as  a  text-book,  it  is  equally  useful  for  the  prac- 
tical farmer.  Profusely  illustrated.  5^2x8  inches.  520 
pages.  Cloth ... 

The  Book  of  Wheat 

By  P.  T.  DONDLINGER.  This  book  comprises  a,  complete 
study  of  everything  pertaining  to  wheat.  It  is  the  work 
of  a  student  of  economic  as  well  as  agricultural  condi- 
tions, well  fitted  by  the  broad  experience  in  both  practical 
and  theoretical  lines  to  tell  the  whole  story  in  a  condensed 
form.  It  is  designed  for  the  farmer,  the  teacher,  and  the 
student  as  well.  Illustrated  5j^x8  inches.  370  pages. 

Cloth.    .    .    .    , , 

(4) 


The  Cereals  in  America 

By  THOMAS  F.  HUNT,  M.S.,  D.Agri,  Professor  of  Agron- 
omy, Cornell  University.  If  you  raise  five  acres  of  any  kind 
of  grain  you  cannot  afford  to  be  without  this  book.  It  is  in 
every  way  the  best  book  on  the  subject  that  has  ever  been 
written.  It  treats  of  the  cultivation  and  improvement  of  everjr 
grain  crop  raised  in  America  in  a  thoroughly  practical  and 
accurate  manner.  The  subject-matter  includes  a  comprehen- 
sive and  succinct  treatise  of  wheat,  maize,  oats,  barley,  rye, 
rice,  sorghum  (kafir  corn)  and  buckwheat,  as  related  particu- 
larly to  American  conditions.  First-hand  knowledge  has  been 
the  policy  of  the  author  in  his  work,  and  every  crop  treated  is 
presented  in  the  light  of  individual  study  of  the  plant.  If  you' 
have  this  book  you  have  the  latest  and  best  that  has  been 
written  upon  the  subject.  Illustrated.  450  pages.  5^x8 
inches.  Cloth 

The  Forage  and  Fiber  Crops  in  America 

By  THOMAS  F.  HUNT.  This  book  is  exactly  what  its  title 
indicates.  It  is  indispensable  to  the  farmer,  student  and 
teacher  who  wishes  all  the  latest  and  most  important  informa- 
tion on  the  subject  of  forage  and  fiber  crops.  Like  its  famous 
companion,  "The  Cereals  in  America,"  by  the  same  author,  it 
treats  of  the  cultivation  and  improvement  of  every  one  of  the 
forage  and  fiber  crops.  With  this  book  in  hand,  you  have 
the  latest  and  most  up-to-date  information  available.  Illus- 
trated. 428  pages.  55/2  x  8  inches.  Cloth 

The  Book  of  Alfalfa 

History,  Cultivation  and  Merits.  Its  Uses  as  a  Forage 
and  Fertilizer.  The  appearance  of  the  Hon.  F.  D.  COBURN'S 
little  book  on  Alfalfa  a  few  years  ago  has  been  a  profit  revela- 
tion to  thousands  of  farmers  throughout  the  country,  and  the 
increasing  demand  for  still  more  information  on  the  subject 
has  induced  the  author  to  prepare  the  present  volume,  which 
is  by  far  the  most  authoritative,  complete  and  valuable  work 
on  this  forage  crop  published  anywhere.  It  is  printed  on  fine 
paper  and  illustrated  with  many  full-page  photographs  that 
were  taken  with  the  especial  view  of  their  relation  to  the  text. 
336  pages.  65^  x  9  inches.  Bound  in  cloth,  with  gold  stamp- 
ing. It  is  unquestionably  the  handsomest  agricultural  refer- 
ence book  that  has  ever  been  issued.  Price,  postpaid,  . 

Clean  Milk 

By  S.  D.  BELCHER,  M.D.  In  this  book  the  author  sets  forth 
practical  methods  for  the  exclusion  of  bacteria  from  milk, 
and  how  to  prevent  contamination  of  milk  from  the  stable 
to  the  consumer.  Illustrated.  5x7  inches.  146  pages. 
Cloth .  - 


Animal  Breeding 

By  THOMAS  SHAW.  This  book  is  the  most  complete  and 
comprehensive  work  ever  published  on  the  subject  of  which 
it  treats.  It  is  the  first  book  which  has  systematized  the  sub- 
ject of  animal  breeding.  The  leading  laws  which  govern  this 
most  intricate  question  the  author  has  boldly  defined  and 
authoritatively  arranged.  The  chapters  which  he  has  written 
on  the  more  involved  features  of  the  subject,  as  sex  and  the 
relative  influence  of  parents,  should  go  far  toward  setting  at 
rest  the  wildly  speculative  views  cherished  with  reference  to 
these  questions.  The  striking  originality  in  the  treatment  of 
the  subject  is  no  less  conspicuous  than  the  superb  order  and 
regular  sequence  of  thought  from  ;he  beginning  to  the  end 
of  the  book.  The  book  is  intended  to  meet  the  needs  of  all 
persons  interested  in  the  breeding  and  rearing  of  live  stock. 
Illustrated.  405  pages.  5x7  inches.  Cloth.  . 

Forage  Crops  Other  Than  Grasses 

By  THOMAS  SHAW.  How  to  cultivate,  harvest  and  use 
them.  Indian  corn,  sorghum,  clover,  leguminous  plants,  crops 
of  the  brassica  genus,  the  cereals,  millet,  field  roots,  etc. 
Intensely  practical  and  reliable.  Illustrated.  287  pages.  5_x  7 
inches.  Cloth 

Soiling  Crops  and  the  Silo 

By  THOMAS  SHAW.  The  growing  and  feeding  of  all  kinds 
of  soiling  crops,  conditions  to  which  they  are  adapted,  their 
plan  in  the  rotation,  etc.  Not  a  line  is  repeated  from  the 
Forage  Crops  book.  Best  methods  of  building  the  silo,  filling 
;t  and  feeding  ensilage.  Illustrated.  364  pages.  5x7  inches. 
Cloth 

The  Study  of  Breeds 

By  THOMAS  SHAW.  Origin,  history,  distribution,  charac- 
teristics, adaptability,  uses,  and  standards  of  excellence  of*all 
pedigreed  breeds  of  cattle,  sheep  and  swine  in  America.  The 
accepted  text  book  in  colleges,  and  the  authority  for 
farmers  and  breeders.  Illustrated.  371  pages.  5x7  inches. 
Cloth 

Clovers  and  How  to  Grow  Them 

By  THOMAS  SHAW.  This  is  the  first  book  published  which 
treats  on  the  growth,  cultivation  and  treatment  of  clovers  as 
applicable  to  all  parts  of  the  United  States  and  Canada,  and 
which  takes  up  the  entire  subject  in  a  systematic  way  and 
consecutive  sequence.  The  importance  of  clover  in  the  econ- 
omy of  the  farm  is  so  great  that  an  exhaustive  work  on  this 
subject  will  no  doubt  be  welcomed  by  students  in  agriculture, 
as  well  as  by  all  who  are  interested  in  the  tilling  of  the  soil. 
Illustrated.  5x7  inches,  337  pages.  Cloth. 

03) 


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